A hybrid distribution transformer integrated with photovoltaic power generation system and control method

Abstract

The application discloses a hybrid power distribution transformer integrated with a photovoltaic power generation system and a control method. The hybrid power distribution transformer integrated with the photovoltaic power generation system comprises a three-winding main transformer, a two-winding auxiliary transformer, a photovoltaic power generation system, a DSP control system, two voltage source inverter systems and a voltage and current sensor module. Through closed-loop control of the two voltage source inverters of the hybrid power distribution transformer integrated with the photovoltaic power generation system, the problems of load distortion, voltage sudden rise and sudden drop and other power quality problems can be solved, the balance of active power of a power distribution node can be dynamically adjusted, reliable access of photovoltaic power and local utilization can be realized, the reactive power of the power distribution node can be dynamically adjusted, the network loss of the active power distribution network can be reduced, the utilization rate of distributed renewable energy can be improved, the use of fossil energy can be saved, pollutants and carbon emissions can be reduced, and the investment cost of the active power distribution network can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of transformer control technology, specifically relating to a hybrid distribution transformer and control method for an integrated photovoltaic power generation system. Background Technology

[0002] With the rapid development of human technology and economy, the demand for energy in modern society is increasing day by day, and the resulting environmental problems and energy crisis are becoming increasingly serious. In order to control greenhouse gas emissions and promote the comprehensive green and low-carbon transformation of the economy and society, the construction of an energy internet that integrates multiple renewable distributed energy sources and realizes cross-regional comprehensive regulation of various forms of energy has become an inevitable development trend.

[0003] The local utilization of distributed renewable energy can reduce energy losses during transmission and improve energy efficiency. However, the large-scale integration of distributed energy sources into the distribution network brings power quality problems such as voltage spikes and drops and harmonic pollution to the user side due to the intermittent and uncertain characteristics of their power generation, as well as the increased use of power electronic devices such as photovoltaic inverters. Voltage fluctuations on the load side can affect the operation of sensitive loads, leading to frequent tripping and malfunctions, thus increasing maintenance costs. Harmonics and nonlinear currents increase network losses and node voltage distortion in the distribution network.

[0004] There are many mature solutions to power quality problems, such as active filters for current power quality problems, dynamic voltage regulators for voltage power quality problems, unified power quality regulators for both voltage and current power quality problems, hybrid distribution transformers, and power electronic transformers.

[0005] However, none of these existing technologies take into account the integration of renewable energy sources such as solar power. This means that when applied to active distribution networks, additional power electronic devices are required to connect the photovoltaic power generation system, increasing equipment costs. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a hybrid distribution transformer and control method for an integrated photovoltaic power generation system, so as to solve the problems in the prior art where additional power electronic devices are required to complete the connection of the photovoltaic power generation system when renewable energy is connected to the distribution network, and the power quality problems exist after the connection.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A hybrid distribution transformer for an integrated photovoltaic power generation system includes a main transformer and an auxiliary transformer. The main transformer includes a primary winding, a secondary winding, and a tertiary winding. The auxiliary transformer includes a quaternary winding and a quinary winding.

[0009] One end of the primary winding and the fifth winding are connected, and the other end of the fifth winding is connected to the medium-voltage distribution network; the secondary winding is connected to the low-voltage distribution network; the tertiary winding is connected to a second power source inverter, and the quaternary winding is connected to a first power source inverter.

[0010] Both the first power inverter and the second power inverter are connected in parallel with the photovoltaic power generation system.

[0011] The first power inverter and the second power inverter are each composed of three power electronic device switch arms connected in parallel; the tertiary winding is connected at the midpoint of the three power electronic device switch arms of the second power inverter, and the quaternary winding is connected at the midpoint of the three power electronic device switch arms of the first power inverter.

[0012] A further improvement of the present invention is that:

[0013] Preferably, the secondary winding is connected to the low-voltage distribution network via a star connection with a neutral line; the 5th winding is connected to the medium-voltage distribution network via a delta connection.

[0014] Preferably, the power electronic device switching bridge arm consists of two IGBTs connected in series.

[0015] Preferably, the fourth winding is connected to the first power source inverter via a filter inductor L1, and the third winding is connected to the second power source inverter via a filter inductor L2.

[0016] Preferably, the first power inverter and the second power inverter are connected through capacitor C. D The photovoltaic power generation system shares a DC bus; it is connected to the DC bus of a unidirectional diode and a power-type inverter.

[0017] A control method for a hybrid distribution transformer in an integrated photovoltaic power generation system obtains the desired DC bus voltage U through a maximum power point tracking algorithm. D *, to achieve the desired DC bus voltage U D * and DC voltage signal U D After subtraction, the difference is input to the third proportional-integral controller to obtain the desired d-axis component i of the grid current. pd *, the desired grid current d-axis component i pd * and the d-axis component of the grid current signal i pdThe difference is calculated and input to the fourth proportional-integral controller to obtain the d-axis component v of the desired output voltage of the second voltage source inverter. 2d *; The d-axis component u of the grid voltage sd The q-axis component i of the grid current pq After multiplying, the result is magnified proportionally by -1.5 times to obtain the reactive power Q of the actual distribution node. s The reactive power Q at the actual power distribution node s and the reactive power Q of the expected distribution node s *Calculate the difference and input the difference value into the fifth proportional-integral controller to obtain the q-axis component v of the desired output voltage of the second voltage source inverter. 2q *; The zero-axis component v of the desired output voltage of the first voltage source inverter. 20 *Set to 0; v 2d *、v 2q * and v 20 After performing an inverse coordinate transformation, the desired output voltage v in the stationary abc coordinate system is obtained. 2a *、v 2b * and v 2c *, v 2a *、v 2b * and v 2c *The gate signal for the second voltage source inverter is obtained through SPWM modulation.

[0018] Preferably, the DC output voltage U of the photovoltaic power generation system is obtained through a voltage and current sensor. pv and DC output current I pv The DC bus voltage U is obtained by combining the maximum power point tracking algorithm and the disturbance analysis method. D *

[0019] Preferably, the desired DC bus voltage U D * and DC voltage signal U D Before the difference is calculated, the DC voltage signal U D High-frequency harmonic components are filtered out using a low-pass filter.

[0020] Preferably, the d-axis component v of the desired output voltage of the first voltage source inverter is... 1d *, q-axis component v 1q * and 0-axis component v 10 After performing an inverse coordinate transformation, the desired output voltage v in the stationary abc coordinate system is obtained. 1a *、v 1b * and v 1c The gate signal for the first voltage source inverter is obtained through SPWM modulation.

[0021] Preferably, the d-axis component v of the desired output voltage of the first voltage source inverter is... 1d The process of obtaining * is as follows: in the dq0 rotating coordinate system, the d-axis component u of the secondary voltage u2 is... 2d With the rated voltage U of the low-voltage distribution network 2N of The difference is multiplied and then input into the first proportional-integral controller to obtain the d-axis component v of the desired output voltage of the first voltage source inverter. 1d *;

[0022] The q-axis component v 1q The process of obtaining * is to obtain the q-axis component u of the secondary voltage u2. 2q The difference is calculated by subtracting the value from the given reference value of 0, and then inputting this difference into the second proportional-integral controller to obtain the q-axis component v of the desired output voltage of the first voltage source inverter. 1q *;

[0023] The 0-axis component v 10 *Set to 0.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention discloses a hybrid distribution transformer integrating a photovoltaic (PV) power generation system. The hybrid distribution transformer includes a three-winding main transformer, a two-winding auxiliary transformer, a PV power generation system, a DSP control system, two voltage source inverter systems, and a voltage and current sensor module. Through closed-loop control of the two voltage source inverters in the hybrid distribution transformer of the integrated PV power generation system, it can solve power quality problems such as load distortion and voltage spikes and drops, dynamically adjust the active power balance of distribution nodes, achieve reliable PV grid connection and local utilization, and dynamically adjust the reactive power of distribution nodes, reducing network losses in the active distribution network, improving the utilization rate of distributed renewable energy, saving fossil fuel use, reducing pollutants and carbon emissions, and lowering the investment cost of the active distribution network.

[0026] This invention also discloses a control method for a hybrid distribution transformer in an integrated photovoltaic power generation system. This control method, through closed-loop control of the two voltage source inverters of the hybrid distribution transformer in the integrated photovoltaic power generation system, can solve power quality problems such as load distortion and voltage surges and drops, dynamically adjust the active power balance of the distribution node to achieve reliable photovoltaic access and local utilization, and dynamically adjust the reactive power of the distribution node to reduce network losses in the active distribution network, improve the utilization rate of distributed renewable energy, save the use of fossil fuels, reduce air pollutants and carbon emissions, and reduce the investment and operating costs of the active distribution network. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of a hybrid distribution transformer for an integrated photovoltaic power generation system according to the present invention.

[0028] Figure 2 This diagram illustrates the control method of the first voltage source inverter 1 in the hybrid distribution transformer of the integrated photovoltaic power generation system involved in this invention.

[0029] Figure 3 This diagram illustrates the control method of the second voltage source inverter 2 in the hybrid distribution transformer of the integrated photovoltaic power generation system involved in this invention.

[0030] Among them, 1-first voltage source inverter; 2-second voltage source inverter; 3-medium voltage distribution network; 4-secondary transformer; 5-main transformer; 6-low voltage distribution network. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0032] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] like Figure 1 As shown, the present invention discloses a hybrid distribution transformer for an integrated photovoltaic power generation system, comprising: a three-winding main transformer 5, a two-winding secondary transformer 4, a photovoltaic power generation system, a DSP control system, two voltage source inverter systems, and a voltage and current sensor module.

[0034] Specifically, the main transformer 5 includes a primary winding W1, a secondary winding W2, and a tertiary winding W3. The auxiliary transformer 4 includes a quaternary winding W4 and a quinary winding W5. Each voltage source inverter system includes six IGBT switching modules. The primary winding W1 of the main transformer 5 and the quinary winding W5 of the auxiliary transformer 4 are connected in series to form the high-voltage winding, which is then connected to the medium-voltage distribution network 3 in a delta configuration. The secondary winding W2 of the main transformer 5 is connected separately to the low-voltage distribution network 6 in a star configuration with a neutral wire, ensuring that electrical energy is transferred from the medium-voltage distribution network 3 to the low-voltage distribution network 6 for user use. The tertiary winding W3 of the main transformer 5 is connected to the second voltage source inverter 2 via a filter inductor L2. By controlling the output voltage of the second voltage source inverter 2, the current in the tertiary winding W3 is controlled. This utilizes the magnetomotive force balance principle to compensate for the distortion and reactive power components in the user-side current, thereby maintaining the sinusoidal current of the primary winding W1 and tracking the specified reactive power. The quaternary winding W4 of the auxiliary transformer 4 is connected to the first voltage source inverter 1 via a filter inductor L1. By controlling the output voltage of the first voltage source inverter 1, the voltage of W5 is controlled, thereby maintaining the sinusoidal current of W2 and keeping it at its rated value. The two voltage source inverters are connected by a large-capacity capacitor C. D They share a DC bus and are connected in parallel. The photovoltaic power generation system connects to the DC bus of the voltage source inverter through a unidirectional diode to ensure the unidirectional flow of active power.

[0035] Each voltage source inverter system consists of three power electronic device switching arms, and each switching arm consists of two IGBT switches connected in series. That is, the voltage source inverter system consists of six IGBT switches. The PWM gating signal issued by the DSP control system is used to control the conduction and cutoff of different arms respectively, thereby obtaining the expected equivalent voltage of the voltage source inverter.

[0036] A photovoltaic panel is connected in series with a diode to ensure unidirectional energy transfer from the photovoltaic panel to the transformer. The photovoltaic panel then connects in parallel with a capacitor and two voltage source inverters to form a DC bus. The main function of the bus capacitor is to store energy and maintain the stability of the bus voltage. The diode is placed in the connection circuit between the photovoltaic panel and the first voltage source inverter 1.

[0037] The control method for the hybrid distribution transformer in an integrated photovoltaic power generation system mainly targets the first voltage source inverter 1 and the second voltage source inverter 2. Firstly, since the proportional-integral controller cannot achieve zero-error following control of a given sinusoidal signal, it is necessary to first control the secondary voltage (u) of the hybrid distribution transformer in the integrated photovoltaic power generation system. 2a ,u 2b ,u 2c ), primary side current (i pa ipb i pc ) and medium-voltage grid voltage (u sa ,u sb ,u sc Perform a rotational coordinate transformation to obtain the equivalent signal quantity in the rotating coordinate system dq0.

[0038] Figure 2 The image shown is designed according to the present invention. Figure 1 The control method of the first voltage source inverter 1. The main function of the first voltage source inverter 1 is to compensate for the fluctuation component of the grid voltage, overcome the power quality problems such as voltage spikes and drops caused by the volatility and randomness of photovoltaic power generation, and ensure that the voltage of the low-voltage distribution network 6 is always maintained at the rated value.

[0039] like Figure 2 As shown, the control method of the first voltage source inverter 1 is as follows: First, in the dq0 rotating coordinate system, the d-axis component u of the secondary voltage u2 is... 2d With low-voltage distribution network 6 voltage rating U 2N of The difference is multiplied and input to the first proportional-integral controller to obtain the d-axis component v of the desired output voltage of the first voltage source inverter 1. 1d Similarly, the q-axis component u of the secondary voltage u2 2q The difference between the value and the given reference value 0 is input to the second proportional-integral controller to obtain the q-axis component v of the desired output voltage of the first voltage source inverter 1. 1q * The q-axis expectation is 0. The 0-axis component v of the expected output voltage of the first voltage source inverter 1. 10 *Set to 0. Then, for the signal quantity v in the dq0 coordinate system of the first voltage source inverter 1... 1d *、v 1q * and v 10 Perform an inverse coordinate transformation to obtain the desired output voltage v in the stationary abc coordinate system. 1a *、v 1b * and v 1c The gate signal for the first voltage source inverter 1 is obtained through SPWM modulation. The DSP control system then controls the switching on and off of the six IGBTs of the first voltage source inverter 1. Furthermore, by switching the six IGBTs on and off, different output voltage values ​​of the first voltage source inverter 1 can be obtained. These different output voltage values ​​control the voltage of the fifth winding W5, thereby ensuring that the output voltage of W2 is sinusoidal and always maintained at its rated value, thus keeping the voltage of the low-voltage distribution network 6 at its rated value.

[0040] Figure 3 The image shown is designed according to the present invention. Figure 1The control method of the second voltage source inverter 2. The second voltage source inverter 2 has the following three main functions: First, it utilizes the DC bus to realize the connection of the photovoltaic power generation system, and uses the outer loop maximum power point tracking algorithm and the DC bus voltage U. D The control system ensures that the photovoltaic power generation system always operates at its maximum power point, maximizing the utilization of distributed photovoltaic energy. Secondly, the inner-loop current control system (fourth proportional-integral control process) suppresses harmonic components in the secondary-side load current. Thirdly, coordinate transformation decouples the active and reactive power control systems, and the primary-side current q-axis component control system (fifth proportional-integral control process) enables continuous dynamic adjustment and zero-steady-state-error control of reactive power at distribution nodes.

[0041] like Figure 3 As shown, the control method for the second voltage source inverter 2 is to obtain the DC output voltage U of the photovoltaic power generation system using voltage and current sensors. pv and current I pv The desired DC bus voltage U under current illumination and temperature conditions is obtained by using the maximum power point tracking algorithm and perturbation analysis. D * The DC voltage signal U acquired by the voltage sensor. D After passing through a low-pass filter to remove high-frequency harmonic components, it is then compared with the desired DC bus voltage U. D The difference is calculated and input into the third proportional-integral controller to obtain the desired d-axis component i of the grid current. pd *, and then compared with the d-axis component i of the acquired grid current signal. pd The difference is calculated and input to the fourth proportional-integral controller to obtain the d-axis component v of the desired output voltage of the second voltage source inverter 2. 2d *. The d-axis component u of the grid voltage. sd The q-axis component i of the grid current pq Multiply the results and then scale them by 1.5 to obtain the reactive power Q at the actual distribution node. s Given the desired reactive power Q at the distribution node. s *With actual reactive power Q s The difference is input into the fifth proportional-integral controller to obtain the q-axis component v of the desired output voltage of the second voltage source inverter 2. 2q *. The zero-axis component v of the desired output voltage of the first voltage source inverter 1. 20 *Set to 0. Then, for the signal quantity v in the dq0 coordinate system of the second voltage source inverter 2... 2d *、v 2q *、v 20 Perform an inverse coordinate transformation to obtain the desired output voltage v in the stationary abc coordinate system.2a *、v 2b * and v 2c * Then, after SPWM modulation, the gate signal of the second voltage source inverter 2 is obtained. The DSP control system controls the turn-on and turn-off of the six IGBTs of the second voltage source inverter 2, thereby controlling the tertiary side current and thus the primary side current.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A control method for a hybrid distribution transformer in an integrated photovoltaic power generation system, characterized in that, Based on a hybrid distribution transformer: including a main transformer (5) and a secondary transformer (4), wherein the main transformer (5) includes a primary winding, a secondary winding and a tertiary winding; and the secondary transformer (4) includes a quaternary winding and a quinary winding; One end of the primary winding and the fifth winding are connected, and the other end of the fifth winding is connected to the medium voltage distribution network (3); the secondary winding is connected to the low voltage distribution network (6); the tertiary winding is connected to a second voltage source inverter (2), and the quaternary winding is connected to a first voltage source inverter (1). Both the first voltage source inverter (1) and the second voltage source inverter (2) are connected in parallel with the photovoltaic power generation system; The first voltage source inverter (1) and the second voltage source inverter (2) are each composed of three power electronic device switch bridge arms connected in parallel; the tertiary winding is connected to the midpoint of the three power electronic device switch bridge arms of the second voltage source inverter (2), and the quaternary winding is connected to the midpoint of the three power electronic device switch bridge arms of the first voltage source inverter (1). The desired DC bus voltage is obtained through the maximum power point tracking algorithm. U D *, to the desired DC bus voltage U D * and DC voltage signal U D After subtraction, the difference is input to the third proportional-integral controller to obtain the desired d-axis component of the grid current. i pd *, the desired d-axis component of the grid current i pd * and the d-axis component of the grid current signal i pd The difference is input to the fourth proportional-integral controller to obtain the d-axis component of the desired output voltage of the second voltage source inverter (2). v 2d *; The d-axis component of the grid voltage u sd q-axis component of grid current i pq After multiplying, the result is magnified proportionally by -1.5 to obtain the reactive power of the actual distribution node. Q s The reactive power of the actual distribution nodes Q s and the reactive power of the expected distribution node Q s *Calculate the difference and input the difference value into the fifth proportional-integral controller to obtain the q-axis component of the desired output voltage of the second voltage source inverter (2). v 2q *; The zero-axis component of the desired output voltage of the second voltage source inverter (1) v 20 *Set to 0; v 2d *、 v 2q *and v 20 After performing an inverse coordinate transformation, the desired output voltage in the stationary abc coordinate system is obtained. v 2a *、 v 2b *and v 2c *,Will v 2a *、 v 2b * and v 2c *The gate signal of the second voltage source inverter (2) is obtained by SPWM modulation; The DC output voltage of the photovoltaic power generation system is obtained through voltage and current sensors. U pv and DC output current I pv The DC bus voltage is obtained by combining the maximum power point tracking algorithm and the disturbance analysis method. U D *; The d-axis component of the desired output voltage of the first voltage source inverter (1) v 1d * q-axis components v 1q * and 0 axis components v 10 After performing an inverse coordinate transformation, the desired output voltage in the stationary abc coordinate system is obtained. v 1a *、 v 1b *and v 1c * The gate signal of the first voltage source inverter (1) is obtained by SPWM modulation; The d-axis component of the desired output voltage of the first voltage source inverter (1) v 1d The process of obtaining * is as follows: in the dq0 rotating coordinate system, the secondary voltage is... u d-axis component of 2 u 2d (6) Voltage rating of low-voltage distribution network U 2N of The difference is multiplied and then input into the first proportional-integral controller to obtain the d-axis component of the desired output voltage of the first voltage source inverter (1). v 1d *; The q-axis component v 1q The process of obtaining * is to obtain the secondary voltage. u q-axis component of 2 u 2q The difference is calculated by subtracting from the given reference value of 0 and inputting the difference into the second proportional-integral controller to obtain the q-axis component of the desired output voltage of the first voltage source inverter (1). v 1q *; The 0-axis component v 10 *Set to 0; The desired DC bus voltage U D * and DC voltage signal U D Before the difference is calculated, the DC voltage signal U D High-frequency harmonic components are filtered out using a low-pass filter.

2. A hybrid distribution transformer for implementing the control method of claim 1 in an integrated photovoltaic power generation system, characterized in that, It includes a main transformer (5) and a secondary transformer (4). The main transformer (5) includes a primary winding, a secondary winding and a tertiary winding; the secondary transformer (4) includes a quaternary winding and a quinary winding. One end of the primary winding and the fifth winding are connected, and the other end of the fifth winding is connected to the medium voltage distribution network (3); the secondary winding is connected to the low voltage distribution network (6); the tertiary winding is connected to a second voltage source inverter (2), and the quaternary winding is connected to a first voltage source inverter (1). Both the first voltage source inverter (1) and the second voltage source inverter (2) are connected in parallel with the photovoltaic power generation system; The first voltage source inverter (1) and the second voltage source inverter (2) are each composed of three power electronic device switch arms connected in parallel; the tertiary winding is connected at the midpoint of the three power electronic device switch arms of the second voltage source inverter (2), and the quaternary winding is connected at the midpoint of the three power electronic device switch arms of the first voltage source inverter (1).

3. The hybrid distribution transformer for an integrated photovoltaic power generation system according to claim 2, characterized in that, The secondary winding is connected to the low-voltage distribution network (6) in a star configuration with a neutral line; the fifth winding is connected to the medium-voltage distribution network (3) in a delta configuration.

4. A hybrid distribution transformer for an integrated photovoltaic power generation system according to claim 2, characterized in that, The power electronic device switching bridge arm consists of two IGBTs connected in series.

5. A hybrid distribution transformer for an integrated photovoltaic power generation system according to claim 2, characterized in that, The fourth winding is connected to a filter inductor. L 1 is connected to the first voltage source inverter (1), and the third-side winding is connected to the filter inductor. L 2. Connect to the second voltage source inverter (2).

6. A hybrid distribution transformer for an integrated photovoltaic power generation system according to claim 2, characterized in that, The first voltage source inverter (1) and the second voltage source inverter (2) are connected by a capacitor. C D A common DC bus is used; the photovoltaic power generation system is connected to the DC bus via a unidirectional diode.

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