Output voltage-sharing control system and method of converter based on IPOS cascade structure

Abstract

The invention relates to an output voltage-sharing control system of a converter based on an IPOS cascade structure. The output voltage-sharing control system comprises a first voltage acquisition module, a second voltage acquisition module, a current acquisition module, a control module and a PWM modulation module, the first voltage acquisition module is connected with the control module and is used for acquiring input voltage at two ends of the full-bridge inverter circuit; the second voltage acquisition module is connected with the control module and is used for acquiring output voltage at two ends of the full-wave rectification circuit; the current acquisition module is connected in series with the output end of the resonant circuit, and the output end of the current acquisition module is connected with the control module for acquiring the output current of the resonant circuit; the control module is connected with the PWM modulation module and is used for outputting a control signal to the PWM modulation module according to the collected voltage and current. The system can effectively utilize clean energy provided by the photovoltaic cell panel, is high in anti-interference capability, is easy to expand, and facilitates the design of a modular system.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converter control, and in particular to an output voltage equalization control system and method of a converter based on an IPOS cascade structure. Background Art

[0002] In recent years, with the intensification of environmental pollution and the significant enhancement of greenhouse gas effects, the new energy field has received unprecedented attention, especially photovoltaic power generation, which is a representative of renewable energy. The total amount of photovoltaic installed capacity accounts for a large proportion of new energy power generation. However, there is a geographical mismatch between power supply and demand, which brings huge challenges to power transmission, such as how to efficiently transmit photovoltaic power generation to demand areas over long distances.

[0003] In photovoltaic power generation systems, in order to achieve the conversion of low-voltage direct current to high voltage to meet the needs of efficient, low-loss long-distance power transmission, an isolated DC / DC converter with a high step-up ratio is required. However, facing the challenge of high-ratio step-up of a single power electronic component, the IPOS system not only achieves efficient voltage boosting but also enhances the stability of the system through the input parallel connection and output series connection of multiple sub-modules.

[0004] In order to ensure the safe and stable operation of the IPOS system, it is necessary to ensure the power balance of each module. The unique structure of the IPOS system ensures that power balance can be achieved as long as the output voltage of each module is balanced, which significantly enhances the safety and stable operation of the system. In the prior art, most scholars have adopted a dual-loop control strategy combining an output voltage loop and an output voltage balancing loop. This strategy uses the master controller to centrally process the output voltage information detected by each module, calculate and generate control signals, and transmit them to each slave controller, and then generate PWM signals to drive the on and off of the switch tube to achieve the stability and balance of the output voltage of each module. Due to differences in manufacturing processes, the resonant parameters of each module are inconsistent, which further increases the difficulty of ensuring the balance of the output voltage of each module. In addition, in the master-slave control architecture, the signal transmission between the master controller and the slave controller is crucial, and the signal delay will affect the real-time response and control accuracy of the system; the failure of the signal transmission line may cause local or overall system instability. In addition, due to the influence of the manufacturing process, the resonant parameters of each module are inconsistent, and ensuring the balance of the output voltage of each module is even more challenging. Summary of the invention

[0005] The present invention proposes an output voltage equalization control system and method of a converter based on an IPOS cascade structure, which solves the technical problems of low anti-interference ability and low safety reliability of the system in the prior art.

[0006] The present invention proposes an output voltage equalization control system of a converter based on an IPOS cascade structure, comprising: a first voltage acquisition module, a second voltage acquisition module, a current acquisition module, a control module and a PWM modulation module;

[0007] The first voltage acquisition module is connected to the control module, and is used to acquire the input voltage at both ends of the full-bridge inverter circuit in the converter with the IPOS cascade structure; the second voltage acquisition module is connected to the control module, and is used to acquire the output voltage at both ends of the full-wave rectifier circuit in the converter with the IPOS cascade structure; the current acquisition module is connected in series to the output end of the resonant circuit in the converter with the IPOS cascade structure, and the output end of the current acquisition module is connected to the control module, and is used to acquire the output current of the resonant circuit; the control module is connected to the PWM modulation module, and is used to output a control signal to the PWM modulation module according to the collected voltage and current; the PWM modulation module is used to output different PWM signals according to the control signal.

[0008] Furthermore, the control module includes: a comparator unit, a dual closed-loop frequency conversion control unit and a phase shift control unit; the comparator unit is connected to the dual closed-loop frequency conversion control unit and the phase shift control unit respectively, and is used to select the dual closed-loop frequency conversion control unit or the phase shift control unit to form a control signal according to the comparison result between the collected input voltage signal and the set voltage threshold.

[0009] Furthermore, the dual closed-loop frequency conversion control unit includes: a voltage feedforward compensation regulator, a voltage closed-loop regulator, a current closed-loop regulator, a first limiter and a voltage-frequency oscillator; the voltage feedforward compensation regulator, the voltage closed-loop regulator, the current closed-loop regulator, the first limiter, the voltage-frequency oscillator and the PWM modulation module are connected in series in sequence; wherein the voltage feedforward compensation regulator is used to obtain the output voltage reference value after feedforward compensation adjustment according to the difference between the output voltage collected by the second voltage collection module and the set output voltage reference value; the voltage closed-loop regulator is used to obtain the resonant current reference value according to the sum of the output voltage reference value after feedforward compensation adjustment and the set output voltage reference value; the current closed-loop regulator is used to obtain the resonant frequency error value according to the difference between the resonant current reference value and the actual resonant current; the first limiter is used to limit the difference between the actual resonant frequency and the resonant frequency error value; the voltage-frequency oscillator is used to generate a control signal, and the control signal controls the formation of four PWM drive signals of the PWM modulation module.

[0010] Further, the phase shift control unit includes: a voltage closed-loop regulator, a second limiter, a first multiplier, a second multiplier, a delay device and a carrier generator; the voltage closed-loop regulator, the second limiter, the first multiplier, the second multiplier, the delay device and the PWM modulation module are connected in series in sequence; the output end of the carrier generator is connected to the PWM modulation module and the delay device respectively; wherein the voltage closed-loop regulator is used to obtain a duty cycle value according to the difference between the output voltage collected by the second voltage collection module and the set output voltage reference value; the second limiter is used to limit the duty cycle value as the duty cycle value of the phase shift; the first multiplier is used to calculate the phase shift angle required for phase shift control according to the duty cycle value of the phase shift; the second multiplier is used to calculate the delay time according to the phase shift angle; the carrier generator forms a control signal for controlling the formation of two PWM drive signals of the PWM modulation module; the delay device is used to delay the control signal formed by the carrier generator according to the delay time to form a delayed control signal to control the formation of the other two PWM drive signals of the PWM modulation module.

[0011] The present invention also provides an output voltage equalization control method of a converter based on an IPOS cascade structure, comprising the following steps:

[0012] Step 1: Use a fixed-frequency asymmetric PWM control method to perform open-loop control on the converter until the voltage is stable;

[0013] Step 2: Get real-time resonant current data, calculate the actual resonant frequency, and update the frequency definition variable in the digital controller to the actual resonant frequency;

[0014] Step 3: Compare the input voltage value with the preset threshold value. According to the comparison result, the system switches to different control strategies.

[0015] Furthermore, in step 3, when the input voltage is less than a preset threshold, a dual closed-loop frequency conversion control strategy is adopted; when the input voltage is greater than the preset threshold, the control mode is switched to a phase shift control mode.

[0016] Furthermore, the dual closed-loop variable frequency control strategy includes the following steps:

[0017] Step S 31 : Obtain the difference between the actual output voltage and the set output voltage reference value as the output voltage error value;

[0018] Step S 32 : The error value of the output voltage is passed through the voltage feedforward compensation regulator to obtain the output voltage reference value after feedforward compensation adjustment;

[0019] Step S 33: The resonant current reference value is obtained by adding the output voltage reference value adjusted by the feedforward compensation and the set output voltage reference value through the voltage closed-loop regulator;

[0020] Step S 34 :Get the difference between the actual resonant current and the resonant current reference value, obtain the resonant frequency error value through the current closed-loop regulator, and make the difference between the actual resonant frequency and the resonant frequency error value to obtain the operating frequency;

[0021] Step S 35 : The operating frequency is limited by the first limiter and output as the input of the voltage-frequency oscillator. The output of the voltage-frequency oscillator obtains the driving signal of each switch tube through the PWM modulation module, controls the on and off of the switch tube, and realizes constant voltage output control.

[0022] Furthermore, the phase shift control strategy includes the following steps:

[0023] Step S 41 : Obtain the difference between the actual output voltage and the set output voltage reference value as the output voltage error value;

[0024] Step S 42 : The error value of the output voltage is obtained through the voltage closed-loop regulator to obtain the duty cycle value, and the duty cycle value of the phase shift is obtained by limiting the amplitude of the second limiter;

[0025] Step S 43 : Calculating the phase shift angle required for phase shift control through a first multiplier according to the duty cycle value of the phase shift;

[0026] Step S 44 : Calculate the delay time through the second multiplier according to the phase shift angle;

[0027] Step S 45 : Delay the control signal generated by the carrier generator through the delay device;

[0028] Step S 46 : The formation of two PWM drive signals in the PWM modulation module is controlled by the control signal generated by the carrier generator; the formation of another two PWM drive signals in the PWM modulation module is controlled by the delayed control signal.

[0029] Beneficial effects obtained by the present invention:

[0030] The output voltage equalization control method of the converter based on the IPOS cascade structure adopted in the present invention reduces the communication between modules compared with other control methods, and each module can operate independently. Each module can adopt a different operating frequency, which solves the output voltage equalization problem of each sub-module of the system when the resonance parameters are inconsistent. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a system block diagram of photovoltaic DC boost collection in a specific embodiment of the present invention;

[0032] Figure 2 It is a structural block diagram of a specific embodiment of the present invention;

[0033] Figure 3 is a schematic diagram of the main circuit of a submodule in a converter in a specific embodiment of the present invention;

[0034] Figure 4 is a method flow chart of a specific embodiment of the present invention;

[0035] Figure 5 is a control block diagram of a specific embodiment of the present invention;

[0036] Figure 6 It is a control block diagram of a dual closed-loop variable frequency control strategy in a specific embodiment of the present invention;

[0037] Figure 7 It is a simulation waveform diagram when the input voltage suddenly changes in a specific embodiment of the present invention;

[0038] Figure 8 It is a simulation waveform diagram when the load suddenly changes in a specific embodiment of the present invention;

[0039] Fig. 9 is a waveform diagram of an open-loop control output voltage when the resonance parameters are inconsistent in a specific embodiment of the present invention;

[0040] Fig.10 is a total output voltage waveform diagram of the method of the present invention when the resonance parameters are inconsistent in a specific embodiment of the present invention;

[0041] Fig.11 It is a waveform diagram of output voltages of various modules of the method of the present invention when the resonance parameters are inconsistent in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0042] The present invention is further explained below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0043] like Figure 1The figure shows a system block diagram for photovoltaic DC boost collection, including: photovoltaic array, Boost converter, low-voltage DC bus, IPOS cascade structure converter, medium-voltage DC bus, DC load, DC grid, inverter. The photovoltaic array adopts a distributed layout, and each photovoltaic module is connected via an independent Boost converter to perform maximum power point tracking (MPPT) to ensure the maximum efficiency of photovoltaic energy conversion. Multiple groups of photovoltaic arrays are connected in parallel to the low-voltage DC bus, and then the voltage on the low-voltage DC bus is boosted with a high transformation ratio through a high-gain isolated DC / DC converter with a cascaded IPOS structure, and finally directly supplied to the DC load or transmitted over a long distance through the DC grid or converted into AC through an inverter to connect to the municipal grid.

[0044] like Figure 2 As shown, it is a structural block diagram of an IPOS cascade structure converter, including: a low-voltage DC bus, a medium-voltage DC bus, and n isolated DC / DC converter submodules, where n is a natural number greater than 1. The main input terminals of the n isolated DC / DC converter submodules are connected in parallel and connected to the low-voltage DC bus, and the auxiliary input terminals are connected in parallel and connected to the low-voltage DC bus; the main output terminals of the n isolated DC / DC converter submodules are connected to the auxiliary output terminals, the main output terminal of the first isolated DC / DC converter submodule is connected to the medium-voltage DC bus, and the auxiliary output terminal of the last isolated DC / DC converter submodule is connected to the medium-voltage DC bus.

[0045] like Figure 3 As shown, the isolated DC / DC converter submodule includes: input filter capacitor C i , full-bridge inverter circuit, resonant circuit, high-frequency transformer T, full-wave rectifier circuit and output filter capacitor C o ; Input filter capacitor C i , full-bridge inverter circuit, resonant circuit, high-frequency transformer T, full-wave rectifier circuit and output filter capacitor C o Connect in parallel.

[0046] The full-bridge inverter circuit is an H-bridge structure, including: four power device switches S1~S4 and four auxiliary capacitors C1~C4; the drain of the power device switch tube S1 is connected to one end of the auxiliary capacitor C1, and the source of the power device switch tube S1 is connected to the other end of the auxiliary capacitor C1; the drain of the power device switch tube S2 is connected to one end of the auxiliary capacitor C2, and the source of the power device switch tube S2 is connected to the other end of the auxiliary capacitor C2; the drain of the power device switch tube S3 is connected to one end of the auxiliary capacitor C3, and the source of the power device switch tube S3 is connected to the other end of the auxiliary capacitor C3; the drain of the power device switch tube S4 is connected to one end of the auxiliary capacitor C4, and the source of the power device switch tube S4 is connected to the auxiliary capacitor C4. The other end of capacitor C4 is connected; the source of power device switch tube S1 is connected to the drain of power device switch tube S3, which is the leading bridge arm of the full-bridge inverter circuit, and the drain of power device switch tube S1 and the source of power device switch tube S3 are the upper and lower ports of the leading bridge arm respectively; the source of power device switch tube S2 is connected to the drain of power device switch tube S4, which is the lagging bridge arm of the full-bridge inverter circuit, and the drain of power device switch tube S2 and the source of power device switch tube S4 are the upper and lower ports of the lagging bridge arm respectively; the leading bridge arm and the lagging bridge arm of the full-bridge inverter circuit are connected in forward parallel, and the two ends of the bridge arm are the input ports of the full-bridge inverter circuit, and the midpoints A and B of the leading bridge arm and the lagging bridge arm are the output ports of the full-bridge inverter circuit.

[0047] The resonant circuit includes: a resonant capacitor C1, a resonant inductor L1, and an excitation inductor L2; the resonant inductor L1 and the resonant capacitor C1 are connected in series and then connected in parallel with the excitation inductor L2. The size of the resonant capacitor C1, the resonant inductor L1 and the excitation inductor L2 determines the resonant frequency of the submodule. The excitation inductor L2 is the self-inductance of the primary winding of the high-frequency transformer T.

[0048] Input filter capacitor C i It is a film capacitor or ceramic capacitor with relatively low withstand voltage and high capacity; the turns ratio of the high-frequency transformer T is: 1:n, which is a step-up high-frequency transformer; the full-wave rectifier circuit is a bridge full-wave rectifier circuit; the output filter capacitor C o It is a film capacitor or ceramic capacitor with high withstand voltage and low capacitance. It should be understood that the preferred embodiment is only for illustrating the present invention, and does not limit the circuit topology of the isolated DC / DC converter submodule applicable to the present invention; wherein, the isolated DC / DC converter submodule adopts a full-bridge LLC resonant converter topology.

[0049] like Figure 5 As shown, the output voltage equalization control system of the converter based on the IPOS cascade structure includes: a first voltage acquisition module, a second voltage acquisition module, a current acquisition module, a control module and a PWM modulation module;

[0050] The first voltage acquisition module is connected in parallel with the input filter capacitor Ci The two ends are connected to the control module to collect the input voltage U at both ends of the full-bridge inverter circuit in the IPOS cascade structure converter. i The second voltage acquisition module is connected in parallel to the output filter capacitor C o The two ends are connected to the control module to collect the output voltage U at both ends of the full-wave rectifier circuit in the IPOS cascade structure converter. o The current acquisition module is connected in series to the output end of the resonant circuit in the converter of the IPOS cascade structure. The output end of the current acquisition module is connected to the control module to collect the resonant current i output by the resonant circuit. L The control module is connected to the PWM modulation module and is used to output a control signal to the PWM modulation module according to the collected voltage and current; the PWM modulation module is used to output different PWM signals according to the control signal.

[0051] like Figure 6 As shown, the control module includes: a comparator unit U1, a dual closed-loop frequency conversion control unit and a phase shift control unit; the comparator unit is connected to the dual closed-loop frequency conversion control unit and the phase shift control unit respectively, and is used to select the dual closed-loop frequency conversion control unit or the phase shift control unit to form a control signal according to the comparison result between the collected input voltage signal and the set voltage threshold.

[0052] The dual closed-loop frequency conversion control unit includes: a voltage feedforward compensation regulator G1, a voltage closed-loop regulator G2, a current closed-loop regulator G3, a first limiter Y1 and a voltage-frequency oscillator VCO; the voltage feedforward compensation regulator G1, the voltage closed-loop regulator G2, the current closed-loop regulator G3, the first limiter Y1, the voltage-frequency oscillator VCO and the PWM modulation module are connected in series in sequence; wherein the voltage feedforward compensation regulator G1 is used to generate a voltage U according to the output voltage U collected by the second voltage collection module o And set the output voltage reference value U o_ref The difference △U is used to obtain the output voltage reference value U after feedforward compensation adjustment. o_ref '; The voltage closed-loop regulator G2 is used to adjust the output voltage reference value U according to the feedforward compensation o_ref ' and set the output voltage reference value U o_ref The sum of the resonant current reference value i is obtained L_ref The current closed-loop regulator G3 is used to adjust the resonant current reference value i L_ref The actual resonant current i L The difference between the resonant frequency error △f is obtained r ; The first limiter Y1 is used to adjust the actual resonant frequency f r ' and the resonant frequency error value △f rThe difference is limited; the voltage-frequency oscillator VCO can generate a sinusoidal carrier signal with a frequency equal to the input value and a signal amplitude range of [1,-1]; when the PWM modulation module is in action, the carrier signal is compared with the modulation signal to generate a drive signal for the switch tube.

[0053] The phase shift control unit includes: a voltage closed-loop regulator G4, a second limiter Y2, a first multiplier X1, a second multiplier X2, a delay device T1 and a carrier generator Z1; the voltage closed-loop regulator G4, the second limiter Y2, the first multiplier X1, the second multiplier X2, the delay device T1 and the PWM modulation module are connected in series in sequence; the output end of the carrier generator Z1 is connected to the PWM modulation module and the delay device T1 respectively; wherein the voltage closed-loop regulator G4 is used to collect the output voltage U according to the second voltage collection module o And set the output voltage reference value U o_ref The duty cycle value is obtained by the difference △U; the second limiter Y2 is used to limit the duty cycle value as the duty cycle value of the phase shift; the first multiplier X1 is used to calculate the phase shift angle required for the phase shift control according to the duty cycle value of the phase shift; the second multiplier X2 is used to calculate the delay time according to the phase shift angle; the carrier generator Z1 forms a control signal to control the formation of two PWM drive signals of the PWM modulation module; the delay device T1 is used to delay the control signal formed by the carrier generator Z1 according to the delay time to form a delayed control signal to control the formation of the other two PWM drive signals of the PWM modulation module. The carrier generator Z1 can emit a triangular carrier signal with a resonant frequency, and the amplitude range of the triangular carrier signal is [1,-1]. The PWM modulation module compares the triangular carrier signal with the modulation signal to generate drive signals PWM1 and PWM3, and compares the delayed triangular carrier signal with the modulation signal to generate drive signals PWM2 and PWM4. The amplitude range of the second limiter Y2 is [0,0.25]. The upper limit of the second limiter Y2 can ensure that the soft switching performance of the submodule is not lost.

[0054] Due to the differences in manufacturing processes, there is a certain degree of deviation in the actual parameter values ​​of electronic components, which leads to inconsistency in the resonance parameters of different modules. Under open-loop control conditions, this parameter difference will cause an imbalance in the output voltage of each module, which will in turn have an adverse effect on the performance and stability of the entire system. In order to solve the problem of output voltage balancing of each sub-module of the IPOS cascade structure converter when the resonance parameters are inconsistent, the following method is proposed: Figure 4 The control flow chart of the , the specific steps are as follows:

[0055] Step S1: In the initial startup phase, the converter is open-loop controlled by a fixed-frequency asymmetric PWM control method, so that the output voltage of the converter gradually increases from zero to a stable voltage, thereby achieving a smooth soft-start process;

[0056] Step S2: When the system output voltage reaches a stable state, the real-time current data is obtained through the built-in resonant current acquisition circuit module of the submodule, and the controller calculates the actual resonant frequency f of the module based on this data. r , and define the frequency variable f in the digital controller r Updated to the calculated resonant frequency f r ';

[0057] Step S3: The system further monitors the input voltage value U through the input voltage acquisition module i and compare it with the preset threshold U i_ref Compare; according to the comparison result, the system switches to different control strategies: when the input voltage is less than the preset threshold U i_ref , a double closed-loop variable frequency control strategy is adopted to adjust the switching frequency of the switch tube in the full-bridge inverter circuit to control the output voltage and maintain it constant; when the input voltage U i Greater than the preset threshold U i_ref , it switches to the phase-shift control mode and maintains the stability of the output voltage by adjusting the conduction time of the switch tube in the full-bridge inverter circuit.

[0058] Once the system output voltage reaches a steady state, Figure 5 The system of the present invention shown in the figure, the current acquisition module in the system obtains real-time resonant current data, calculates and updates the frequency definition variable f in the controller r is the actual resonant frequency f r '. Then, the first voltage acquisition module is used to obtain the input voltage U i and the preset threshold U i_ref Compare and switch different control strategies according to the comparison results to ensure constant voltage control of each sub-module output.

[0059] The dual closed-loop frequency conversion control strategy includes the following steps:

[0060] Step S 31 :Get the actual output voltage U o And set the output voltage reference value U o_ref The difference is taken as the error value △U of the output voltage;

[0061] Step S 32 :The output voltage error value △U is obtained through the voltage feedforward compensation regulator G1 to obtain the output voltage reference value U after feedforward compensation adjustment o_ref ';

[0062] Step S 33 :The output voltage reference value U after feedforward compensation adjustment o_ref ' and set the output voltage reference Uo_ref The sum of the resonant current reference value i is obtained through the voltage closed-loop regulator G2 L_ref ;

[0063] Step S 34 :Get the actual resonant current i L and the resonant current reference value i L_ref The difference is calculated and the resonant frequency error value △f is obtained through the current closed-loop regulator G3. r , the actual resonant frequency f r ' and the resonant frequency error value △f r Make the difference and get the operating frequency f s ;

[0064] Step S 35 :The operating frequency f s The limiting output of the first limiter Y1 is used as the input of the voltage-frequency oscillator VCO. The output of the voltage-frequency oscillator VCO obtains the driving signal of each switch tube through the PWM modulation module, controls the on and off of the switch tube, and realizes constant voltage output control.

[0065] The phase shift control strategy includes the following steps:

[0066] Step S 41 :Get the actual output voltage U o And set the output voltage reference value U o_ref The difference is taken as the error value △U of the output voltage;

[0067] Step S 42 : The error value △U of the output voltage is obtained through the voltage closed-loop regulator G4 to obtain the duty cycle value, and the duty cycle value of the phase shift is obtained after the second limiter Y2 is limited;

[0068] Step S 43 : The duty cycle value of the phase shift is used as the first input of the first multiplier X1, and π is used as the second input of the first multiplier X1. The phase shift angle required for phase shift control is obtained through calculation by the first multiplier X1;

[0069] Step S 44 :Use the phase shift angle required for phase shift control as the first input of the second multiplier X2, and use 1 / 2πf r 'As the second input of the second multiplier X2, the delay time is obtained after calculation by the second multiplier X2;

[0070] Step S 45 : The control signal generated by the carrier generator Z1 is delayed by the delay device T1;

[0071] Step S 46: The formation of the PWM1 and PWM3 drive signals in the PWM modulation module is controlled by the control signal generated by the carrier generator Z1; the formation of the other two PWM2 and PWM4 drive signals in the PWM modulation module is controlled by the delayed control signal.

[0072] The IPOS combined system simulation model consisting of three sub-modules is built in Simulink to verify the reasonable stability of an output voltage equalization control method of a converter based on the IPOS cascade structure. The specific simulation parameters of a single module are shown in Table 1:

[0073]

[0074]

[0075] Table 1

[0076] For a single module, in actual operation, when a PV array fails, the input voltage will drop sharply. At this time, it is necessary to ensure that the converter can operate normally and stably when a failure occurs. Assuming that the input voltage suddenly changes from 40V to 36V in 0.2s, Figure 7 It can be seen that when the input voltage suddenly changes, the output voltage of the single module rises and stabilizes at 240V after a short voltage drop.

[0077] Figure 8 The simulation waveform diagram of a single module in Matlab / Simulink when the load suddenly changes. When the output load suddenly changes from 240Ω to 120Ω in 0.2s, it can be seen from the output waveform in the figure that after the load suddenly changes, the converter output voltage can still be stabilized at 240V, indicating that the control strategy can effectively cope with the working conditions of load sudden changes.

[0078] When the resonant inductor L of submodule 1 r1 =5uH, submodule 2 resonant inductor L r2 =5.5uH, submodule 3 resonant inductor L r3 =4.5uH, at this time, the output voltage waveform of each sub-module of the combined converter in open-loop control is shown in Fig. 9 From the figure, it can be seen that the output voltages of the submodules under open-loop control are unbalanced, which are 239.3V, 233.1V, and 244.8V respectively. When the system is converted from the traditional open-loop control to the output voltage equalization control method proposed in the present invention, Fig.10 The system output voltage waveform shows that the system output gradually stabilizes at 720V. Fig.11 From the output voltage waveforms of each sub-module, it can be observed that the output voltage of each sub-module shows an obvious equilibrium trend, and finally reaches a stable equilibrium state at the time point of 0.12s.

[0079] In summary, the output voltage equalization control method of the converter based on the IPOS cascade structure disclosed in the present invention can simplify the control structure of the sub-modules. The sub-modules do not need to communicate with each other and can operate independently, which effectively solves the problem of unbalanced output voltage of the sub-modules due to inconsistent resonant parameters, and improves the anti-interference ability and performance of the converter.

Claims

1. An output voltage equalization control system of a converter based on an IPOS cascade structure, characterized in that: include: A first voltage acquisition module, a second voltage acquisition module, a current acquisition module, a control module and a PWM modulation module; The first voltage acquisition module is connected to the control module and is used to acquire the input voltage at both ends of the full-bridge inverter circuit in the converter with the IPOS cascade structure; the second voltage acquisition module is connected to the control module and is used to acquire the output voltage at both ends of the full-wave rectifier circuit in the converter with the IPOS cascade structure; The current acquisition module is connected in series to the output end of the resonant circuit in the converter of the IPOS cascade structure. The output end of the current acquisition module is connected to the control module for collecting the output current of the resonant circuit; the control module is connected to the PWM modulation module for outputting a control signal to the PWM modulation module according to the collected voltage and current; The PWM modulation module is used to output different PWM signals according to the control signal.

2. The output voltage equalization control system of the converter based on the IPOS cascade structure according to claim 1, characterized in that: The control module includes: a comparator unit, a dual closed-loop frequency conversion control unit and a phase shift control unit; the comparator unit is connected to the dual closed-loop frequency conversion control unit and the phase shift control unit respectively, and is used to select the dual closed-loop frequency conversion control unit or the phase shift control unit to form a control signal according to the comparison result between the collected input voltage signal and the set voltage threshold.

3. The output voltage equalization control system of the converter based on the IPOS cascade structure according to claim 2, characterized in that: The dual closed-loop frequency conversion control unit includes: a voltage feedforward compensation regulator, a voltage closed-loop regulator, a current closed-loop regulator, a first limiter and a voltage-frequency oscillator; the voltage feedforward compensation regulator, the voltage closed-loop regulator, the current closed-loop regulator, the first limiter, the voltage-frequency oscillator and the PWM modulation module are connected in series in sequence; wherein the voltage feedforward compensation regulator is used to obtain the output voltage reference value after feedforward compensation adjustment according to the difference between the output voltage collected by the second voltage collection module and the set output voltage reference value; the voltage closed-loop regulator is used to obtain the resonant current reference value according to the sum of the output voltage reference value after feedforward compensation adjustment and the set output voltage reference value; the current closed-loop regulator is used to obtain the resonant frequency error value according to the difference between the resonant current reference value and the actual resonant current; the first limiter is used to limit the difference between the actual resonant frequency and the resonant frequency error value; the voltage-frequency oscillator is used to generate a control signal, and the control signal controls the formation of four PWM drive signals of the PWM modulation module.

4. The output voltage equalization control system of the converter based on the IPOS cascade structure according to claim 2 or 3, characterized in that: The phase shift control unit comprises: a voltage closed-loop regulator, a second limiter, a first multiplier, a second multiplier, a delay device and a carrier generator; the voltage closed-loop regulator, the second limiter, the first multiplier, the second multiplier, the delay device and the PWM modulation module are connected in series in sequence; the output end of the carrier generator is connected to the PWM modulation module and the delay device respectively; wherein the voltage closed-loop regulator is used to obtain a duty cycle value according to the difference between the output voltage collected by the second voltage collection module and the set output voltage reference value; the second limiter is used to limit the duty cycle value as the duty cycle value of the phase shift; the first multiplier is used to calculate the phase shift angle required for phase shift control according to the duty cycle value of the phase shift; the second multiplier is used to calculate the delay time according to the phase shift angle; the carrier generator forms a control signal for controlling the formation of two PWM drive signals of the PWM modulation module; the delay device is used to delay the control signal formed by the carrier generator according to the delay time to form a delayed control signal to control the formation of the other two PWM drive signals of the PWM modulation module.

5. A method for controlling output voltage equalization of a converter based on an IPOS cascade structure, applied to the output voltage equalization control system of a converter based on an IPOS cascade structure as claimed in any one of claims 1 to 4, characterized in that: The method comprises the following steps: Step 1: Use a fixed-frequency asymmetric PWM control method to perform open-loop control on the converter until the voltage is stable; Step 2: Get real-time resonant current data, calculate the actual resonant frequency, and update the frequency definition variable in the digital controller to the actual resonant frequency; Step 3: Compare the input voltage value with the preset threshold value. According to the comparison result, the system switches to different control strategies.

6. The output voltage equalization control method of the converter based on the IPOS cascade structure according to claim 5, characterized in that: In step 3, when the input voltage is less than a preset threshold, a dual closed-loop frequency conversion control strategy is adopted; when the input voltage is greater than the preset threshold, the control mode is switched to a phase shift control mode.

7. The output voltage equalization control method of the converter based on the IPOS cascade structure according to claim 6, characterized in that: The dual closed-loop frequency conversion control strategy includes the following steps: Step S 31 : Obtain the difference between the actual output voltage and the set output voltage reference value as the output voltage error value; Step S 32 : The error value of the output voltage is passed through the voltage feedforward compensation regulator to obtain the output voltage reference value after feedforward compensation adjustment; Step S 33 : The resonant current reference value is obtained by adding the output voltage reference value adjusted by the feedforward compensation and the set output voltage reference value through the voltage closed-loop regulator; Step S 34 :Get the difference between the actual resonant current and the resonant current reference value, obtain the resonant frequency error value through the current closed-loop regulator, and make the difference between the actual resonant frequency and the resonant frequency error value to obtain the operating frequency; Step S 35 : The operating frequency is limited by the first limiter and output as the input of the voltage-frequency oscillator. The output of the voltage-frequency oscillator obtains the driving signal of each switch tube through the PWM modulation module, controls the on and off of the switch tube, and realizes constant voltage output control.

8. The output voltage equalization control method of the converter based on the IPOS cascade structure according to claim 6 or 7, characterized in that: The phase shift control strategy comprises the following steps: Step S 41 : Obtain the difference between the actual output voltage and the set output voltage reference value as the output voltage error value; Step S 42 : The error value of the output voltage is obtained through the voltage closed-loop regulator to obtain the duty cycle value, and the duty cycle value of the phase shift is obtained by limiting the amplitude of the second limiter; Step S 43 : Calculating the phase shift angle required for phase shift control through a first multiplier according to the duty cycle value of the phase shift; Step S 44 : Calculate the delay time through the second multiplier according to the phase shift angle; Step S 45 : Delay the control signal generated by the carrier generator through the delay device; Step S 46 : The formation of two PWM drive signals in the PWM modulation module is controlled by the control signal generated by the carrier generator; the formation of another two PWM drive signals in the PWM modulation module is controlled by the delayed control signal.

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