Single-phase voltage stabilizer and control method and system thereof

Abstract

The invention discloses a single-phase voltage stabilizing device and a control method and system thereof. Compared with a traditional single-phase full-bridge PWM rectifier and a single-phase full-bridge inverter, the single-phase voltage stabilizing device has the advantages that one bridge arm is reduced, the device cost is lower, fewer devices are needed, fault nodes are correspondingly reduced, and the reliability is higher. The problem of control coupling of a grid-connected input side and an inverter output side is caused due to the fact that one bridge arm is shared, the inverter output side voltage is given to be associated with a grid side, the phases of the inverter output side voltage and the grid side are synchronized, then pulses of the shared bridge arm are naturally decoupled, and the output sinusoidal voltage is obtained. Meanwhile, due to the full-bridge PWM rectification control mode adopted by the grid-connected input side, the grid-side power factor can be 1, and the grid-side current is sinusoidal, so that green grid connection of the device is realized; the inverter output side tracks the network side voltage and introduces the direct current bus voltage as negative feedback, so that the stability of the output voltage is ensured, the stable single-phase voltage output is finally obtained, and the quality of the power supply electric energy in the substation is improved.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics, and in particular relates to a single-phase voltage stabilizing device and a control method and system thereof. Background Art

[0002] Traction power supply substations play a crucial role in the railway power supply system and are a crucial component in the development of modern railway traction power. Traction power supply substations typically draw power from three-phase high voltage or the overhead catenary. Under normal conditions, the three-phase high voltage is stepped down, but in the event of a high voltage fault, the power is automatically transferred to the overhead catenary's single-phase supply.

[0003] At present, there are power quality problems in the on-site power supply of the traction power supply substation. Specifically, the power quality of the contact network power supply is poor, the voltage fluctuates violently and there are many harmonics, which can easily cause damage to some electrical equipment.

[0004] In order to improve the quality of power supply within the station, it is urgently necessary to develop a single-phase voltage stabilizing device to solve the power supply problems within the above-mentioned traction power supply division station. Summary of the Invention

[0005] The purpose of the present invention is to provide a single-phase voltage stabilization device and its control method and system, which are used to improve the safety of equipment operation in traction power supply substations, while also improving the power factor on the grid side, thereby achieving green grid connection for the device. The present invention reduces the cost of the voltage stabilization device by reusing bridge arms. To address the power coupling issues of reused bridge arms and single-phase input and output, a predictive control approach that treats the input and output as a whole is adopted, thereby achieving decoupling of input and output control. To address the problem of traditional input controlled rectifier control requiring a phase-locked loop to calculate the grid voltage angle, which is computationally intensive, a method that substitutes the instantaneous grid value into the calculation is adopted, achieving effective controlled rectifier control without a phase-locked loop.

[0006] The technical solutions provided by the present invention are as follows:

[0007] In a first aspect, the present invention provides a single-phase voltage stabilizing device, the device comprising:

[0008] The grid-connected input side includes a bridge arm a and a bridge arm b; wherein: the bridge arm a is composed of a first power switch device S1 and a second power switch device S2 connected in series, and the bridge arm b is composed of a third power switch device S3 and a fourth power switch device S4 connected in series; the series connection point of the first power switch device S1 and the second power switch device S2 in the bridge arm a is connected to a grid-side inductor L and an equivalent resistor R, and the other end of the grid-side inductor L is connected to one end of the single-phase grid; the series connection point of the third power switch device S3 and the fourth power switch device S4 in the bridge arm b is connected to the other end of the single-phase grid;

[0009] The equivalent resistance R is the total equivalent resistance including the internal resistance of the single-phase grid, the parasitic resistance of the grid-side line and the inductive resistance;

[0010] The bridge arm b is also multiplexed as an output bridge arm;

[0011] The inverter output side includes a bridge arm c and a reused bridge arm b; wherein: the bridge arm c is composed of a fifth power switch device S5 and a sixth power switch device S6 connected in series, and the series connection point is connected to the filter inductor L f ;Filter inductor L f The other end is connected to the filter capacitor C f One end of the filter capacitor C f The other end is connected to the series connection point of the third power switch device S3 and the fourth power switch device S4 of the bridge arm b;

[0012] DC link unit, including DC bus capacitor C dc The DC bus capacitor C dc Connected in parallel between the common connection points of the power devices of bridge arm a, bridge arm b and bridge arm c;

[0013] Filter and output unit, including filter inductor L f and filter capacitor C f , the filter inductor L f With filter capacitor C f After being connected in series, they are connected between bridge arm c and reuse bridge arm b;

[0014] Load equivalent resistance R L , connected in parallel with the filter capacitor C f The two ends of the load voltage u o and load current i o .

[0015] In one embodiment, the switch state of each bridge arm is S x ∈{0, 1}, x∈{a, b, c} produces two valid switching states, and the DC bus voltage is constant at u dc , then these two switching states will produce an output voltage u xo ∈{-u dc ,0,u dc}.

[0016] In one embodiment, the switching state of the multiplexing bridge arm b determines that the input and output voltages must operate in a small phase difference state, that is, when the switching state of the multiplexing bridge arm b is 1, the third power switch device S3 is turned on, and the input and output voltages are -u dc Or 0; when the switch state of the multiplexed bridge arm b is 0, the fourth power switch device S4 is turned on, and the input and output voltages are u dc or 0.

[0017] In one embodiment, the relationship between the input and output voltages and the three bridge arm switch states Sa, Sb, and Sc is:

[0018] When the three-arm switch state is (0,0,0), the input voltage is 0 and the output voltage is 0;

[0019] When the three-arm switch state is (1,0,0), the input voltage u dc , output voltage 0;

[0020] When the three-arm switch state is (1, 0, 1), the input voltage u dc , output voltage u dc ;

[0021] When the three-arm switch state is (0,0,1), the input voltage is 0 and the output voltage is u dc ;

[0022] When the three-arm switch state is (0,1,1), the input voltage -u dc , output voltage 0;

[0023] When the three-arm switch state is (0,1,0), the input voltage -u dc , output voltage -u dc ;

[0024] When the three-arm switch state is (1,1,0), the input voltage is 0 and the output voltage is -u dc ;

[0025] When the three-arm switch state is (1,1,1), the input voltage is 0 and the output voltage is 0.

[0026] In a second aspect, the present invention provides a control method for a single-phase voltage stabilizing device, the method comprising:

[0027] Real-time collection of grid-side voltage, grid-side current, DC bus voltage, inverter output-side current and voltage of single-phase voltage stabilization device;

[0028] The difference between the DC bus voltage set value and the actual DC bus voltage value is input into the voltage PI regulator. The output of the PI regulator is multiplied by the adjustment coefficient k1 and then multiplied by the grid-side voltage to obtain the grid-side current set value.

[0029] The grid-side voltage is multiplied by the adjustment coefficient k2 as the inverter output-side voltage set value. The difference between the inverter output-side voltage set value and the actual output-side voltage value is input into the output voltage deadbeat controller. The output of the deadbeat controller is used as the inverter output-side current set value.

[0030] The adjustment coefficient

[0031] The adjustment coefficient

[0032] Among them, P oN Output rated power of single-phase voltage stabilizing device, e a is the grid side voltage, u dc is the DC bus voltage;

[0033] The grid-side current set value, the inverter output-side current set value and the actual grid-side current value and the inverter output-side current value are subtracted and input into the predictive controller. By considering the input and output as a whole, a predictive control model of the single-phase voltage stabilizing device is constructed.

[0034] Construct an evaluation function based on the prediction model of the single-phase voltage stabilizing device;

[0035] The evaluation function is optimized by rolling optimization to obtain the optimal switching states of bridge arms a, b, and c.

[0036] In one embodiment, the grid-side current set value, the inverter output-side current set value, and the collected grid-side current value and inverter output-side current value are subtracted and input into a predictive controller, and the input and output are considered as a whole to construct a predictive control model of the single-phase voltage stabilizing device, including:

[0037] Equating the grid-connected input side to a single-phase PWM rectifier and ignoring the equivalent resistance R, the voltage equation is:

[0038] Equating the inverter output side to a single-phase voltage source inverter, the KVL and KCL equations are listed as:

[0039]

[0040] According to the relationship between the input and output voltages and the three-arm switch states Sa, Sb, and Sc, the voltage u in the voltage equation is converted to ab The voltage u in KVL and KCL equations cb are expressed by the switch state, i.e. u ab =Su dc 、u cb =S′u dc , Su dc with S′u dc There are three states: 0, 1, and -1;

[0041] Replace u in the voltage equation, KVL, and KCL equations ab with u cb After expressing it in terms of switch states, the prediction model of the single-phase voltage stabilization device is obtained by discretizing it using forward Euler:

[0042]

[0043] Where i a (k+1),u o (k+1) and i(k+1) are the grid-side current, output voltage, and output-side current prediction values, respectively. a (k),u o (k), i(k) are the grid-side current, output voltage and current value of output-side current respectively, T s is the sampling period, L is the grid-side inductance, C f is the filter capacitor, e a (k) is the current value of the grid-side voltage, i o (k) is the current value of the load current.

[0044] In one embodiment, the evaluation function is:

[0045]

[0046] Where i a (k+1), u0(k+1), and i(k+1) are the grid-side current, output voltage, and output-side current prediction values, respectively. i * They are the grid-side current, output voltage and output-side current given values respectively.

[0047] In one embodiment, in order to eliminate the beat delay, a beat is predicted forward one more time, and the current value at the k+2th moment of the next cycle is predicted for control. The prediction model of the single-phase voltage stabilizing device at the k+2th moment is expressed as:

[0048]

[0049] Where i a (k+1),u o (k+1) and i(k+1) are the grid-side current, output voltage, and output-side current prediction values, respectively. a (k),u o (k), i(k) are the grid-side current, output voltage and current value of output-side current respectively, T s is the sampling period, L is the grid-side inductance, C f is the filter capacitor, e a (k) is the current value of the grid-side voltage, i o (k) is the current value of the load current;

[0050] The evaluation function is:

[0051]

[0052] Where i a (k+2),uo i(k+2) and i(k+2) are the grid-side current, output voltage and output-side current prediction values at time k+2, respectively. i * They are the grid-side current, output voltage and output-side current given values respectively.

[0053] In one embodiment, the step of performing rolling optimization on the evaluation function to obtain the optimal switching states of the bridge arms a, b, and c includes:

[0054] According to the input side prediction model, the corresponding input voltage values of the four states of bridge arm a and b switch states Sa and Sb (0,0), (0,1), (1,0), and (1,1) are substituted in turn to obtain the predicted grid side current i a (k+1), choose The switch state with the smallest value is determined, and the switch state of the multiplexing bridge arm b is determined;

[0055] Substitute the output voltage values corresponding to the switch states Sa of the bridge arm c at 0 and 1 into the output side prediction model to obtain the predicted output voltage u o (k+1) and the output current i(k+1), and select the switching state that minimizes the evaluation function g.

[0056] In a third aspect, the present invention provides a control system for a single-phase voltage stabilizing device, the system comprising:

[0057] The acquisition module is used to collect the grid-side voltage, grid-side current, DC bus voltage, inverter output-side current and output voltage of the single-phase voltage stabilization device in real time;

[0058] The grid-side current reference value calculation module is used to calculate the difference between the DC bus voltage set value and the actual DC bus voltage value. The difference is input into the voltage PI regulator. The output of the PI regulator is multiplied by the adjustment coefficient k1 and then multiplied by the grid-side voltage to obtain the grid-side current set value.

[0059] The inverter output side current setting calculation module is used to multiply the grid side voltage by the adjustment coefficient k2 as the inverter side output voltage setting value. The difference between the inverter output side voltage setting value and the actual output side voltage value is input into the output voltage deadbeat controller. The output of the deadbeat controller is used as the inverter output side current setting value.

[0060] The adjustment coefficient

[0061] The adjustment coefficient

[0062] Among them, P oN Output rated power of single-phase voltage stabilizing device, e a is the grid side voltage, u dcis the DC bus voltage;

[0063] A prediction model building module is used to input the difference between the grid-side current set value, the inverter output-side current set value and the actual grid-side current value and the inverter output-side current value into the prediction controller, and to build a prediction control model for the single-phase voltage stabilizing device by considering the input and output as a whole;

[0064] An evaluation function construction module, used to construct an evaluation function based on a prediction model of a single-phase voltage stabilizing device;

[0065] The optimization module is used to perform rolling optimization on the evaluation function to obtain the optimal switching states of bridge arms a, b, and c.

[0066] Beneficial effects of the present invention:

[0067] The device of the present invention has a simple structure. Compared with the traditional single-phase full-bridge PWM rectifier + single-phase full-bridge inverter structure, it reduces one bridge arm, has lower device cost, requires fewer devices, and has correspondingly fewer fault nodes, and has higher reliability. Since a bridge arm is shared, the control coupling problem of the grid-connected input side and the inverter output side is brought about. The present invention achieves the acquisition of the output sinusoidal voltage by associating the given voltage of the inverter output side with the grid side and synchronizing their phases, thereby naturally decoupling the pulses of the shared bridge arm. At the same time, due to the full-bridge PWM rectifier control mode adopted by the grid-connected input side, the grid-side power factor can be 1, and the grid-side current is sinusoidal, realizing green grid connection of the device; the inverter output side tracks the grid-side voltage and introduces the DC bus voltage as negative feedback to ensure the stability of the output voltage, and finally obtains a stable single-phase voltage output, thereby improving the power quality of the power supply within the station. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The accompanying drawings, as part of this disclosure, are intended to provide a further understanding of the disclosure. The exemplary embodiments of the disclosure and their descriptions are intended to explain the disclosure and do not constitute undue limitations thereon. Obviously, the drawings described below are merely examples, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0069] Figure 1 A topological diagram of a single-phase voltage stabilizing device provided in one embodiment of the present invention;

[0070] Figure 2 This is a working mode diagram of a single-phase voltage stabilizing device under eight switching states provided in one embodiment of the present invention;

[0071] Figure 3 is a space vector generated on a space plane by a single-phase voltage stabilizing device provided in one embodiment of the present invention;

[0072] Figure 4 A flow chart of a control method for a single-phase voltage stabilizing device according to an embodiment of the present invention;

[0073] Figure 5 This is an operating waveform diagram of a single-phase voltage stabilizing device using the control method of the present invention provided in one embodiment of the present invention.

[0074] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0075] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0076] In order to deepen the knowledge and understanding of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0077] Reference Figure 1 As shown, an embodiment of the present invention provides a single-phase voltage stabilizing device, the device comprising:

[0078] The grid-connected input side includes a bridge arm a and a bridge arm b; wherein: the bridge arm a is composed of a first power switch device S1 and a second power switch device S2 connected in series, and the bridge arm b is composed of a third power switch device S3 and a fourth power switch device S4 connected in series; the series connection point of the first power switch device S1 and the second power switch device S2 in the bridge arm a is connected to a grid-side inductor L and an equivalent resistor R, and the other end of the grid-side inductor L is connected to one end of the single-phase grid; the series connection point of the third power switch device S3 and the fourth power switch device S4 in the bridge arm b is connected to the other end of the single-phase grid;

[0079] The equivalent resistance R is the total equivalent resistance including the internal resistance of the single-phase grid, the parasitic resistance of the grid-side line and the inductive resistance;

[0080] The bridge arm b is also multiplexed as an output bridge arm;

[0081] The inverter output side includes a bridge arm c and a reused bridge arm b; wherein: the bridge arm c is composed of a fifth power switch device S5 and a sixth power switch device S6 connected in series, and the series connection point is connected to the filter inductor L f ;Filter inductor L f The other end is connected to the filter capacitor C f One end of the filter capacitor C f The other end is connected to the series connection point of the third power switch device S3 and the fourth power switch device S4 of the bridge arm b;

[0082] DC link unit, including DC bus capacitor C dc The DC bus capacitor C dc Connected in parallel between the common connection points of the power devices of bridge arm a, bridge arm b and bridge arm c;

[0083] Filter and output unit, including filter inductor L f and filter capacitor C f , the filter inductor L f With filter capacitor C f After being connected in series, they are connected between bridge arm c and reuse bridge arm b;

[0084] Load equivalent resistance R L , connected in parallel with the filter capacitor C f The two ends of the load voltage u o and load current i o .

[0085] Furthermore, the switch state of each bridge arm of the single-phase voltage stabilizing device is S x ∈{0, 1}, x∈{a, b, c} produces two valid switching states. Assume that the DC bus voltage is constant at u dc , then these two switching states will produce an output voltage (voltage at terminals a and b) of u xo ∈{-u dc ,0,u dc}.

[0086] The input and output voltages generated by the single-phase voltage stabilization device are related to the switching states of the three bridge arms (S a , S b , S c ) is shown in Table 1.

[0087] Table 1 Relationship between input and output voltage and the switch state of the three bridge arms

[0088]

[0089] As can be seen from Table 1, the polarity of the input and output voltages is determined by the switching state of the multiplexed bridge arm.

[0090] Furthermore, the switching state of the multiplexing bridge arm b determines that the input and output voltages must operate in a small phase difference state, that is, when the switching state of the multiplexing bridge arm b is 1, the third power switch device S3 is turned on, and the input and output voltages are -u dc Or 0; when the switch state of the multiplexed bridge arm b is 0, the fourth power switch device S4 is turned on, and the input and output voltages are u dc or 0.

[0091] The switching states of the three bridge arms have 8 possible switching combinations. Figure 2The working mode diagrams of the voltage stabilizer under 8 switching combinations are given. If the three bridge arm branches are regarded as an integral unit, then all the instantaneous voltages generated by the single-phase voltage stabilizer can be represented by the vector sum of the input and output voltages, and the voltage U is defined as ab and U cb Coincident with the real axis and imaginary axis in the vector plane respectively, the instantaneous voltage generated by the single-phase voltage stabilizing device can be described as:

[0092]

[0093] The space vectors generated by all switch combinations can be expressed in the space plane as Figure 3 As shown, the 6 effective vectors divide the entire space plane into six sectors N = 1 to 6, U n-ref In a switching cycle T s Reference voltage generated in inner sector N.

[0094] The single-phase voltage stabilizing device can be divided into the grid-connected input side and the inverter output side. Since the grid-connected input side and the inverter output side share the b bridge arm, the switching state is coupled. The coupling problem can be solved by reasonably selecting the control scheme.

[0095] The single-phase voltage stabilizing device can be divided into the grid-connected input side and the inverter output side. Since the grid-connected input side and the inverter output side share the b bridge arm, the switching states are coupled and need to be decoupled through a suitable pulse width control strategy to achieve high power factor, AC / DC voltage conversion and DC voltage stabilization functions on the input side, while achieving stable AC voltage output to the external load.

[0096] In one embodiment, a control method for a single-phase voltage stabilizing device is proposed, such as Figure 4 As shown, the method includes:

[0097] Step S100: Real-time acquisition of the grid-side voltage e of the single-phase voltage stabilizing device a , grid-side current i a , DC bus voltage u dc , inverter output side current i and output voltage u o .

[0098] Step S200: Set the DC bus voltage to a given value u dc_ref and the actual DC bus voltage u dc The difference is input into the voltage PI regulator, and the output of the PI regulator is multiplied by the adjustment coefficient k1 and then multiplied by the grid-side voltage e a As the grid-side current given value.

[0099] Furthermore, the adjustment coefficient k1 (k1>0) is determined by the following formula:

[0100]

[0101] Where, P oN is the rated output power of the device, e a is the grid side voltage.

[0102] Step S300: The grid-side voltage e a Multiply by the adjustment coefficient k2 (k2>0) as the inverter output voltage given value Set the inverter output voltage to a given value and the actual output voltage u o The difference is input into the output voltage deadbeat controller, and the output of the deadbeat controller is used as the given value of the inverter output current i * .

[0103] Furthermore, the adjustment coefficient k2 (k2>0) is determined by the following formula:

[0104]

[0105] Where u dc is the DC bus voltage.

[0106] Step S400: Subtract the grid-side current set value, the inverter output-side current set value from the actual grid-side current value and the inverter output-side current value, and input the result into the prediction controller. By considering the input and output as a whole, a prediction control model of the single-phase voltage stabilizing device is constructed.

[0107] In the embodiment of the present application, the specific implementation steps of step S400 are as follows:

[0108] Step S410: Equating the grid-connected input side to a single-phase PWM rectifier and ignoring the equivalent resistance R, thereby obtaining a voltage equation.

[0109] Specifically, the grid-connected input side can be regarded as a single-phase PWM rectifier, and its voltage equation can be expressed as:

[0110]

[0111] Since the equivalent resistance R is small, it can generally be ignored. After sorting, the voltage equation can be obtained as follows:

[0112]

[0113] Step S420: Equating the inverter output side to a single-phase voltage source inverter, and listing KVL and KCL equations.

[0114] Combine Figure 1 Listing these KVL and KCL equations, we can obtain:

[0115]

[0116] Step S430: According to the relationship between the input and output voltages and the three-arm switch states Sa, Sb, and Sc, the voltage u in the voltage equation is converted to ab The voltage u in KVL and KCL equations cb are expressed by the switch state, i.e. u ab =Su dc 、u cb =S′u dc , Su dc with S′u dc There are three states: 0, 1, and -1. The three-arm switch states corresponding to each state are shown in Table 1.

[0117] Step S440: Substitute u in the voltage equation, KVL and KCL equations ab with u cb After being expressed in terms of switch states, the prediction model of the single-phase voltage stabilizing device is obtained by discretizing it using forward Euler.

[0118] That is, u in formula (5) and formula (6) ab with u cb Expressed in terms of switch states, and discretized using forward Euler, we can obtain:

[0119]

[0120]

[0121] Where i a (k+1),u o (k+1) and i(k+1) are the grid-side current, output voltage, and output-side current prediction values, respectively. a (k),u o (k), i(k) are the grid-side current, output voltage and current value of output-side current respectively, T s is the sampling period, L is the grid-side inductance, C f is the filter capacitor, e a (k) is the current value of the grid-side voltage, i o (k) is the current value of the load current.

[0122] Step S500: constructing an evaluation function based on the prediction model of the single-phase voltage stabilizing device.

[0123] In order to select the appropriate switching state, it is necessary to define an objective function to evaluate the predicted value, and then select the optimal switching state by minimizing the objective function. The present invention uses the variance function as the evaluation function, and considers the input and output as a whole to construct the evaluation function to achieve decoupling control.

[0124] Furthermore, the evaluation function g is:

[0125]

[0126] Where i a (k+1), u0(k+1), and i(k+1) are the grid-side current, output voltage, and output-side current prediction values, respectively. i * They are the grid-side current, output voltage and output-side current given values respectively.

[0127] Typically, because the predicted current and evaluation function need to be calculated in each sampling cycle, a considerable amount of computation time is required from the start of sampling to the solution of the optimal modulation function. If the computation time is too long, the resulting modulation function will not be used until the next cycle.

[0128] In an optional embodiment, in order to eliminate the beat delay, a beat is predicted forward again, and the current value at the k+2th moment of the next cycle is predicted for control. The prediction model of the single-phase voltage stabilizing device at the k+2th moment is expressed as:

[0129]

[0130] Where i a (k+1),u o (k+1) and i(k+1) are the grid-side current, output voltage, and output-side current prediction values, respectively. a (k),u o (k), i(k) are the grid-side current, output voltage and current value of output-side current respectively, T s is the sampling period, L is the grid-side inductance, C f is the filter capacitor, e a (k) is the current value of the grid-side voltage, i o (k) is the current value of the load current.

[0131] Similarly, the evaluation function in formula (9) should be rewritten as:

[0132]

[0133] Where i a (k+2),u o i(k+2) and i(k+2) are the grid-side current, output voltage and output-side current prediction values at time k+2, respectively. i * They are the grid-side current, output voltage and output-side current given values respectively.

[0134] Step S600: performing rolling optimization on the evaluation function to obtain the optimal switching states of bridge arms a, b, and c.

[0135] In the embodiment of the present application, the evaluation function is subjected to rolling optimization to obtain the optimal switching states of bridge arms a, b, and c. The specific steps include:

[0136] According to the input side prediction model, the corresponding input voltage values of the four states of bridge arm a and b switch states Sa and Sb (0,0), (0,1), (1,0), and (1,1) are substituted in turn to obtain the predicted grid side current i a (k+1), choose The switch state with the smallest value is determined, and the switch state of the multiplexing bridge arm b is determined;

[0137] Substitute the output voltage values corresponding to the switch states Sa of the bridge arm c at 0 and 1 into the output side prediction model to obtain the predicted output voltage u o (k+1) and the output current i(k+1), and select the switching state that minimizes the evaluation function g.

[0138] In order to ensure that the voltage stabilizing device can achieve unity power factor, the present invention generally requires a phase-locked loop to lock the phase of the grid-side voltage, which undoubtedly increases the computational burden. The present invention designs a relatively simple implementation method. For the rectifier side, the output of the regulator is multiplied by a regulation coefficient k1 related to the grid-side voltage as the grid-side current reference value. Since the grid-side voltage contains phase information, it can be ensured that the voltage stabilizing device can still operate at unity power factor without using a phase-locked loop. In the calculation of the coefficient k1, the absolute value of the grid-side voltage is introduced as the denominator, eliminating the impact of the DC bus voltage fluctuation of twice the power frequency introduced by single-phase rectification on the DC bus voltage control. For the inverter output side, the same method is used to multiply the grid-side voltage by the related regulation coefficient k2 as the output voltage reference value, so that the output voltage and the input voltage remain in phase, avoiding the problem that the input and output cannot be completely independently controlled due to the reuse of the bridge arm, while avoiding the use of complex phase-locked loop operations.

[0139] In addition, during the operation of the single-phase voltage stabilizing device provided by the present invention, due to the single-phase rectification, the DC bus has a voltage fluctuation of 2 times the frequency. If the output voltage does not take this fluctuation into account, the output voltage will be distorted. The present invention introduces the adjustment coefficient k2, which is used to calculate the DC bus voltage u dc Substituting the values into the calculation, we can actually realize the real-time feedback of the DC bus voltage, eliminating the influence of the DC bus voltage double frequency fluctuation on the output voltage.

[0140] Figure 5The figure shows the simulation waveforms of the single-phase voltage stabilizing device and control method proposed in the present invention. As can be seen from the figure, due to the adoption of single-phase rectification control, the voltage and current on the grid side are in phase, and the power factor is close to 1. The grid-side current waveform is sinusoidal, with low harmonic content, and does not "pollute" the power grid. Due to the use of single-phase rectification and inversion, there is a 2-fold frequency fluctuation in the DC bus, but due to the introduction of the DC bus regulation coefficient k2, the mean value of the DC bus voltage fluctuates around the given voltage 370V, and the control does not diverge due to the existence of the 2-fold frequency fluctuation. Since the output voltage is controlled by model prediction, the output voltage waveform is sinusoidal and load-friendly. As can be seen from the figure, since the input and output voltages are almost in phase, it can fully support the reuse of hardware bridge arms, realize low-cost, high-performance single-phase rectification and inversion control, and achieve green grid connection.

[0141] In one embodiment, a control system for a single-phase voltage stabilizing device is provided, the system comprising:

[0142] The acquisition module is used to collect the grid-side voltage, grid-side current, DC bus voltage, inverter output-side current and output voltage of the single-phase voltage stabilization device in real time;

[0143] The grid-side current reference value calculation module is used to calculate the difference between the DC bus voltage set value and the actual DC bus voltage value. The difference is input into the voltage PI regulator. The output of the PI regulator is multiplied by the adjustment coefficient k1 and then multiplied by the grid-side voltage to obtain the grid-side current set value.

[0144] The inverter output side current setting calculation module is used to multiply the grid side voltage by the adjustment coefficient k2 as the inverter side output voltage setting value. The difference between the inverter output side voltage setting value and the actual output side voltage value is input into the output voltage deadbeat controller. The output of the deadbeat controller is used as the inverter output side current setting value.

[0145] Adjustment coefficient

[0146] Adjustment coefficient

[0147] Among them, P oN Output rated power of single-phase voltage stabilizing device, e a is the grid side voltage, u dc is the DC bus voltage;

[0148] A prediction model building module is used to input the difference between the grid-side current set value, the inverter output-side current set value and the actual grid-side current value and the inverter output-side current value into the prediction controller, and to build a prediction control model for the single-phase voltage stabilizing device by considering the input and output as a whole;

[0149] An evaluation function construction module, used to construct an evaluation function based on a prediction model of a single-phase voltage stabilizing device;

[0150] The optimization module is used to perform rolling optimization on the evaluation function to obtain the optimal switching states of bridge arms a, b, and c.

[0151] It should be noted that the control system of the single-phase voltage stabilizing device provided in the above embodiment only uses the division of the above-mentioned functional modules as an example when executing the control method of the single-phase voltage stabilizing device. In actual applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above. In addition, the control system of the single-phase voltage stabilizing device provided in the above embodiment and the control method embodiment of the single-phase voltage stabilizing device belong to the same concept. The implementation process thereof is detailed in the control method embodiment of the single-phase voltage stabilizing device and will not be repeated here.

[0152] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with this patent can make slight changes or modifications to equivalent embodiments using the above-mentioned technical contents without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the invention without departing from the content of the technical solution of the present invention are still within the scope of the present invention.

Claims

1. A single-phase voltage stabilizing device, characterized in that: The device includes: The grid-connected input side includes a bridge arm a and a bridge arm b; wherein: the bridge arm a is composed of a first power switch device S1 and a second power switch device S2 connected in series, and the bridge arm b is composed of a third power switch device S3 and a fourth power switch device S4 connected in series; the series connection point of the first power switch device S1 and the second power switch device S2 in the bridge arm a is connected to a grid-side inductor L and an equivalent resistor R, and the other end of the grid-side inductor L is connected to one end of the single-phase grid; the series connection point of the third power switch device S3 and the fourth power switch device S4 in the bridge arm b is connected to the other end of the single-phase grid; The equivalent resistance R is the total equivalent resistance including the internal resistance of the single-phase grid, the parasitic resistance of the grid-side line and the inductive resistance; The bridge arm b is also multiplexed as an output bridge arm; The inverter output side includes a bridge arm c and a reused bridge arm b; wherein: the bridge arm c is composed of a fifth power switch device S5 and a sixth power switch device S6 connected in series, and the series connection point is connected to the filter inductor L f ;Filter inductor L f The other end is connected to the filter capacitor C f One end of the filter capacitor C f The other end is connected to the series connection point of the third power switch device S3 and the fourth power switch device S4 of the bridge arm b; DC link unit, including DC bus capacitor C dc The DC bus capacitor C dc Connected in parallel between the common connection points of the power devices of bridge arm a, bridge arm b and bridge arm c; Filter and output unit, including filter inductor L f and filter capacitor C f , the filter inductor L f With filter capacitor C f After being connected in series, they are connected between bridge arm c and reuse bridge arm b; Load equivalent resistance R L , connected in parallel with the filter capacitor C f The two ends of the load voltage u o and the load current i o .

2. A single-phase voltage stabilizing device according to claim 1, characterized in that: Each bridge arm switch state S x ∈{0, 1}, x∈{a, b, c} produces two valid switching states, and the DC bus voltage is constant at u dc , then these two effective switching states will produce an output voltage u xo ,u xo ∈{-u dc ,0,u dc }.

3. A single-phase voltage stabilizing device according to claim 2, characterized in that: The switching state of the multiplexing bridge arm b determines that the input and output voltages must operate in a small phase difference state, that is, when the switching state of the multiplexing bridge arm b is 1, the third power switch device S3 is turned on, and the input and output voltages are -u dc Or 0; when the switch state of the multiplexed bridge arm b is 0, the fourth power switch device S4 is turned on, and the input and output voltages are u dc or 0.

4. A single-phase voltage stabilizing device according to claim 3, characterized in that: The relationship between the three bridge arm switch states Sa, Sb, Sc and the input and output voltages is: When the three-arm switch state is (0,0,0), the input voltage is 0 and the output voltage is 0; When the three-arm switch state is (1,0,0), the input voltage u dc , output voltage 0; When the three-arm switch state is (1, 0, 1), the input voltage u dc , output voltage u dc ; When the three-arm switch state is (0,0,1), the input voltage is 0 and the output voltage is u dc ; When the three-arm switch state is (0,1,1), the input voltage -u dc , output voltage 0; When the three-arm switch state is (0,1,0), the input voltage -u dc , output voltage -u dc ; When the three-arm switch state is (1,1,0), the input voltage is 0 and the output voltage is -u dc ; When the three-arm switch state is (1,1,1), the input voltage is 0 and the output voltage is 0.

5. A control method for a single-phase voltage stabilizing device, characterized in that: The method comprises: Real-time collection of grid-side voltage, grid-side current, DC bus voltage, inverter output-side current and voltage of single-phase voltage stabilization device; The difference between the DC bus voltage set value and the actual DC bus voltage value is input into the voltage PI regulator. The output of the PI regulator is multiplied by the adjustment coefficient k1 and then multiplied by the grid-side voltage to obtain the grid-side current set value. The grid-side voltage is multiplied by the adjustment coefficient k2 as the inverter output-side voltage set value. The difference between the inverter output-side voltage set value and the actual output-side voltage value is input into the output voltage deadbeat controller. The output of the deadbeat controller is used as the inverter output-side current set value. The adjustment coefficient The adjustment coefficient Among them, P oN Output rated power of single-phase voltage stabilizing device, e a is the grid side voltage, u dc is the DC bus voltage; The grid-side current set value, the inverter output-side current set value and the actual grid-side current value and the inverter output-side current value are subtracted and input into the predictive controller. By considering the input and output as a whole, a predictive control model of the single-phase voltage stabilizing device is constructed. Construct an evaluation function based on the prediction model of the single-phase voltage stabilizing device; The evaluation function is optimized by rolling optimization to obtain the optimal switching states of bridge arms a, b, and c.

6. The control method of a single-phase voltage stabilizing device according to claim 5, characterized in that: The subtraction of the grid-side current set value, the inverter output-side current set value and the actual grid-side current value and the inverter output-side current value is input into the prediction controller, and the prediction control model of the single-phase voltage stabilizing device is constructed by considering the input and output as a whole, including: Equating the grid-connected input side to a single-phase PWM rectifier and ignoring the equivalent resistance R, the voltage equation is: Equating the inverter output side to a single-phase voltage source inverter, the KVL and KCL equations are listed as: According to the input and output voltages and the three-arm switch state S a 、S b 、S c The voltage u in the voltage equation is ab The voltage u in KVL and KCL equations cb are expressed by the switch state, i.e. u ab =Su dc 、u cb =S′u dc , Su dc with S'u dc There are three states: 0, 1, and -1; Replace u in the voltage equation, KVL, and KCL equations ab with u cb After expressing it in terms of switch states, the prediction model of the single-phase voltage stabilization device is obtained by discretizing it using forward Euler: Where i a (k+1),u o (k+1) and i(k+1) are the grid-side current, output voltage, and output-side current prediction values, respectively. a (k),u o (k), i(k) are the grid-side current, output voltage and current value of output-side current respectively, T s is the sampling period, L is the grid-side inductance, C f is the filter capacitor, e a (k) is the current value of the grid-side voltage, i o (k) is the current value of the load current.

7. The control method of a single-phase voltage stabilizing device according to claim 6, characterized in that: The evaluation function is: Where i a (k+1),u o (k+1) and i(k+1) are the grid-side current, output voltage and output-side current prediction values respectively. i * They are the grid-side current, output voltage and output-side current given values respectively.

8. The control method of a single-phase voltage stabilizing device according to claim 6, characterized in that: In order to eliminate the beat delay, we predict one beat ahead and use the current value at the k+2th moment in the next cycle for control. The prediction model of the single-phase voltage stabilizer at the k+2th moment is expressed as: Where i a (k+1),u o (k+1) and i(k+1) are the grid-side current, output voltage, and output-side current prediction values, respectively. a (k),u o (k), i(k) are the grid-side current, output voltage and current value of output-side current respectively, T s is the sampling period, L is the grid-side inductance, C f is the filter capacitor, e a (k) is the current value of the grid-side voltage, i o (k) is the current value of the load current; The evaluation function is: Where i a (k+2),u o i(k+2) and i(k+2) are the grid-side current, output voltage and output-side current prediction values at time k+2, respectively. i * They are the grid-side current, output voltage and output-side current given values respectively.

9. A control method for a single-phase voltage stabilizing device according to claim 7 or 8, characterized in that: The rolling optimization of the evaluation function to obtain the optimal switching states of the bridge arms a, b, and c specifically includes the following steps: According to the input side prediction model, the switch states of bridge arms a and b are S a 、S b Substitute the corresponding input voltage values in the four states (0,0), (0,1), (1,0), and (1,1) in turn to obtain the predicted grid-side current i a (k+1), choose The switch state with the smallest value is determined, and the switch state of the multiplexing bridge arm b is determined; Substitute the output voltage values corresponding to the switch states Sa of the bridge arm c at 0 and 1 into the output side prediction model to obtain the predicted output voltage u o (k+1) and the output current i(k+1), and select the switching state that minimizes the evaluation function g.

10. A control system for a single-phase voltage stabilizing device, characterized in that: The system comprises: The acquisition module is used to collect the grid-side voltage, grid-side current, DC bus voltage, inverter output-side current and output voltage of the single-phase voltage stabilization device in real time; The grid-side current reference value calculation module is used to calculate the difference between the DC bus voltage set value and the actual DC bus voltage value. The difference is input into the voltage PI regulator. The output of the PI regulator is multiplied by the adjustment coefficient k1 and then multiplied by the grid-side voltage to obtain the grid-side current set value. The inverter output side current setting calculation module is used to multiply the grid side voltage by the adjustment coefficient k2 as the inverter side output voltage setting value. The difference between the inverter output side voltage setting value and the actual output side voltage value is input into the output voltage deadbeat controller. The output of the deadbeat controller is used as the inverter output side current setting value. The adjustment coefficient The adjustment coefficient Among them, P oN Output rated power of single-phase voltage stabilizing device, e a is the grid side voltage, u dc is the DC bus voltage; A prediction model building module is used to calculate the difference between the grid-side current set value, the inverter output-side current set value and the actual grid-side current value and the inverter output-side current value, and input the difference into the prediction controller. By considering the input and output as a whole, a prediction control model of the single-phase voltage stabilization device is constructed. An evaluation function construction module, used to construct an evaluation function based on a prediction model of a single-phase voltage stabilizing device; The optimization module is used to perform rolling optimization on the evaluation function to obtain the optimal switching states of bridge arms a, b, and c.

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