CN202353232U - High-voltage cascaded inverter power unit grid-connection feedback device - Google Patents

Abstract

The utility model discloses a grid-connected feedback device for a power unit of a high-voltage cascaded frequency converter, which includes an incoming line switch. The power unit to be aged is connected, the phase-shifted grid-connected transformer is connected to the grid-connected switch at the same time, the grid-connected switch is connected to the grid-connected reactor, and the grid-connected reactor is connected to the three power units to be aged respectively. The sampling part includes three grid-connected windings. Phase voltage sampling, output voltage sampling of the power unit and output current sampling of the power unit, the sampling signals of the three-phase voltage sampling of the grid-connected winding, the output voltage sampling of the power unit and the output current sampling of the power unit are sent to the control system, The sampling signal is processed by the control system. The utility model realizes the purpose of power unit aging, and at the same time can save energy and reduce consumption; the utility model occupies a small area and has strong operability, and can perform aging of three power units at the same time, thereby improving production efficiency.

Description

A high-voltage cascaded inverter power unit grid-connected feedback device

technical field

The utility model relates to a high-voltage cascaded frequency converter power unit aging experiment technology, more specifically, relates to a high-voltage cascaded frequency converter power unit grid-connected feedback device.

Background technique

With the development of power electronics technology, cascaded high-voltage inverters are widely used in electric power, metallurgy, petrochemical, tap water, coal and other fields, saving a lot of electric energy and creating considerable economic and social benefits.

In order to ensure the reliability of the product, the aging test of the power unit must be carried out before the high-voltage cascaded inverter leaves the factory, that is, the power unit works at the rated current for a period of time. In the high-voltage cascaded inverter industry, there are two main aging methods for power units: resistive load aging and reactor load aging. Resistive loads are generally composed of several power resistors connected in series and in parallel, and different resistance values are achieved through series and parallel connections to adapt to the output current values of different power units. Each resistor platform often requires a large space and high heat dissipation requirements, and a large amount of electric energy is wasted on the heating of the resistors. The aging of the inductive load requires matching the inductance value for the output current value of the power module. The above two kinds of load aging are inefficient and occupy a huge space.

Figure 1 shows the electrical schematic diagram of traditional load aging. The three-phase power input is converted into DC by the rectifier diode of the power unit, and converted into a 0-50Hz AC power output by the inverter of the H-bridge of the power unit, and the output voltage is applied to a resistive load or an inductive load; it is adjusted by changing the impedance of the load The size of the output current achieves the purpose of aging. The traditional load aging mode takes up a lot of space and is complicated to adjust, requiring high professional quality of commissioning personnel; moreover, the traditional load aging cost is high and the operability is poor, which is not suitable for the production requirements of modern automation enterprises.

Utility model content

The main problem to be solved by the utility model is to propose a new type of power unit aging device, which is convenient to control, strong in applicability and high in aging efficiency.

The technical scheme adopted by the utility model to solve the above problems is described as follows:

A high-voltage cascaded inverter power unit grid-connected feedback device, including an incoming line switch, characterized in that: the incoming line switch is connected to a phase-shifting grid-connected transformer, and the phase-shifting grid-connected transformer is connected to three power units to be aged , the phase-shifted grid-connected transformer is connected to the grid-connected switch at the same time, the grid-connected switch is connected to the grid-connected reactor, and the grid-connected reactor is connected to the three aging power units respectively. The sampling part includes the three-phase voltage sampling of the grid-connected winding, power The output voltage sampling of the unit and the output current sampling of the power unit, the sampling signals of the three-phase voltage sampling of the grid-connected winding, the output voltage sampling of the power unit and the output current sampling of the power unit are sent to the control system, and the sampling The signal is processed.

The incoming line switch is used to connect the power grid and the phase-shifting grid-connected transformer. When the system fails, the incoming line switch is automatically disconnected to protect against the expansion of the accident.

The phase-shifting grid-connected transformer integrates five windings, reducing the size of the whole device. Among them, the power supply winding is connected with the incoming line switch, and its capacity is selected as 10% of the total capacity. The power supply winding plays the role of system reactive power and supplementary active power loss; there are 3 phase-shifting windings, and the phase of each winding is -20°, respectively. 0°, 20°, respectively connected to 3 different power units. The phase-shifting winding of the transformer and the power unit form an 18-pulse rectifier. Through the phase-shifting of the transformer, the harmonic content of the current on the power supply side is minimized, and the harmonic pollution to the power grid is reduced. The capacity of each phase-shifting winding is the total capacity The grid-connected winding is connected to the grid-connected switch to recycle the power fed back by the power module, and the capacity is 100%.

In the power unit, the inputs of the three power units are respectively connected to the phase-shifting windings of the transformer, and the rectification type is a three-phase full-bridge uncontrollable rectification; the output of the three power units is an H-bridge type, and the V of the three H-bridges The output terminals are connected together to form a neutral point, and the three Us respectively form three-phase voltage ABC output, which are respectively connected to the grid-connected reactor; the power unit is connected to the control system through an optical fiber, and the real-time operation information and fault information are transmitted to the control system. system. The DC link of the power unit is connected with an electrolytic capacitor. The DC bus has a pre-charging circuit composed of silicon controlled rectifiers, absorbing resistors, and absorbing capacitors.

The grid-connected reactor is connected to the U terminals of the three power units and the grid-connected switch. The grid-connected reactor is a three-phase adjustable reactor, and the inductance value of the reactor is adjusted according to the current value of the power unit, which plays the role of power transmission and filtering. At the same time, ensure that the current harmonics output by the power unit under different powers are less than the standard value.

The grid-connected switch is connected to the grid-connected reactor and the winding of the grid-connected transformer. Grid-connected switch control is realized by the control system.

The sampling part is connected to the power loop and the control system. The sampling part mainly includes the three-phase voltage sampling of the grid-connected winding, the output voltage sampling of the power unit and the output current sampling of the power unit. The sampling part sends these signals to the control system, and the control system processes these signals.

The control system, which is connected to the sampling part and the power unit, is composed of a sampling processing and grid-connected control unit, a calculation unit, a pulse control unit, and a man-machine interface. The control system processes the voltage and current of the sampling part; through the calculation unit, the current control algorithm based on PI control in the synchronous rotating coordinate system feeds back the energy absorbed by the power unit to the grid, and the grid supplements the system power loss and reactive power at the same time. The calculation result is output to the pulse control unit for pulse management, and communicates with the power unit through optical fiber, transmits control signals and receives operating information of the power unit, etc.; the man-machine interface can set different parameters to achieve different aging current controls.

The aforementioned control method in the control system of the high-voltage cascaded inverter power unit grid-connected feedback device includes a current control algorithm based on PI control, and is characterized in that it includes the following steps:

1) Phase-lock the sampled grid voltage to obtain grid voltage angle θ, and vector decouple the grid voltage and output current to obtain grid voltage active component E _d , grid voltage reactive component E _q , grid current active component i _d , grid The current reactive component i _q , the initial grid current active component _id is _compared with the given value idref of the active component, and the difference obtained is output by the PI controller;

2) Compare the output voltage value with the grid voltage active component E _d , i _q ωL (ω is the angular frequency, L is the inductance value of the output reactor) to obtain the reference voltage active component u _dref ;

3) Similarly, the initial grid current reactive component i _q is compared with the reactive component given value i _qref , and the difference obtained from the comparison is output by the PI controller, and the obtained voltage value and the voltage reactive component E _q , i _d ωL Comparing to obtain the reference voltage reactive component u _qref ;

4) performing inverse transformation on the obtained u _dref and u _qref to obtain a three-phase reference voltage;

5) The pulse control unit forms a PWM pulse according to the three-phase reference voltage, and sends the PWM pulse to the power unit through an optical fiber.

The grid-connected feedback device of the power unit of the high-voltage cascaded frequency converter of the utility model replaces the traditional load aging device, and feeds back most of the energy to the power grid. It can save energy and reduce consumption. In addition, the device of the utility model has the advantages of small volume, convenient control, strong applicability and high aging efficiency.

Description of drawings

Figure 1 Electrical schematic diagram of traditional load aging;

Figure 2 Electrical structure diagram of power unit;

Fig. 3 electrical schematic diagram of the utility model;

Figure 4 control system control schematic diagram;

Figure 5 system control flow chart.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the utility model is further described:

As shown in Figure 3, the utility model is a high-voltage cascaded inverter power unit grid-connected feedback device, including an incoming line switch, a phase-shifting grid-connected transformer, a power module, a grid-connected reactor, a grid-connected switch, a sampling part, a control system.

First, set the required aging current through the man-machine interface, and the control system selects the inductance value of the grid-connected reactor according to the aging current.

After a certain period of time, the control system closes the incoming line switch, and the grid voltage passes through the incoming line switch to the power winding of the phase-shifting grid-connected transformer, and supplies the DC bus of the power unit for charging. After a period of time the thyristor conducts. This kind of rectification constitutes 18-pulse rectification, which reduces the harmonic pollution of the grid current. The control system controls the H-bridge of the power unit to convert the DC power into 50Hz single-phase AC power. The V terminals of the power unit output are connected to form a common point, and the U terminals form ABC three-phase.

At the same time, the control system judges the frequency, amplitude, and phase of the voltage at both ends by collecting the voltage on both sides of the grid-connected switch. After the relationship between the three meets a certain relationship, the control system controls the grid-connected switch to close, and the entire system is successfully connected to the grid. After the system is successfully connected to the grid, the control system performs current control according to the aging current set by the man-machine interface.

The specific control process is shown in Figure 5. The control system adopts the current control algorithm based on PI control in the synchronous rotating coordinate system: the calculation unit phase-locks the collected grid-connected winding voltage, and outputs the grid voltage angle θ; the voltage and output current are transformed by clark and park to obtain E _d , E _q , i _d , i _q . The initial current id is compared with the given value _idref , and the resulting difference is output by the PI controller. _The output voltage value is compared with the grid voltage active component E _d , i _q ωL to obtain the reference voltage active component u _dref . Similarly, the initial current i _q is compared with the given value i _qref , and the difference obtained from the comparison is output by the PI controller, and the obtained voltage value is compared with the voltage reactive component E _q and i _d ωL to obtain the reference voltage reactive component u _qref . The obtained reference voltages u _dref and u _qref are inversely transformed by park and clark to obtain ABC three-phase reference voltages, which are sent to the pulse control unit for pulse distribution to form three-phase PWM signals. The PWM signal is transmitted to the three power units by the control system through the optical fiber to control the opening and closing of the IGBT on the power unit, so that the power unit outputs a three-phase voltage, which is connected to the grid-connected winding of the transformer after passing through the grid-connected reactor, and feeds back to the grid energy.

At the same time, the power grid provides energy to the three power units through the rectification link through the phase-shifted winding of the transformer, forming a closed loop of energy. The grid compensates for power losses throughout the system.

The beneficial effects of the utility model are: strong operability, good control performance, high reliability; high electric energy feedback rate, remarkable energy-saving effect; small occupied area, three power unit aging experiments can be carried out at the same time, greatly improving production efficiency , creating considerable economic value.

Claims (6)

1. A high-voltage cascaded frequency converter power unit grid-connected feedback device, including an incoming line switch, characterized in that: the incoming line switch is connected to a phase-shifting grid-connected transformer, and the phase-shifting grid-connected transformer is respectively connected to three aging power The units are connected, the phase-shifted grid-connected transformer is connected to the grid-connected switch at the same time, the grid-connected switch is connected to the grid-connected reactor, and the grid-connected reactor is connected to the three aging power units respectively. The sampling part includes the three-phase voltage sampling of the grid-connected winding , the output voltage sampling of the power unit and the output current sampling of the power unit, the sampling signals of the three-phase voltage sampling of the grid-connected winding, the output voltage sampling of the power unit and the output current sampling of the power unit are sent to the control system, and the control system Process the sampled signal. 2. The high-voltage cascaded inverter power unit grid-connected feedback device according to claim 1, characterized in that: the phase-shifted grid-connected transformer integrates 5 windings, wherein the power supply winding is connected to the incoming line switch, and the phase-shifting winding 3 in total, each winding phase is -20°, 0°, 20° respectively, connected to 3 different power units respectively, the phase-shifting winding of the transformer and the power unit form an 18-pulse rectification, and the grid-connected winding is connected to the parallel network switch. 3. The high-voltage cascaded inverter power unit grid-connected feedback device according to claim 2, characterized in that: the inputs of the three power units are respectively connected to the phase-shifting windings of the transformer, and the rectification type is a three-phase full bridge Uncontrollable rectification; the output of the three power units is H-bridge type, the V output terminals of the three H-bridges are connected together to form a neutral point, and the three Us form a three-phase voltage ABC output, respectively connected to the grid reactor Above; each power unit is connected to the control system through an optical fiber, and the control system transmits real-time operation information and fault information. 4. The grid-connected feedback device for the power unit of the high-voltage cascaded frequency converter according to claim 3, wherein the DC link of the power unit adopts three sets of electrolytic capacitors connected in series. 5. The grid-connected feedback device of the power unit of the high-voltage cascaded frequency converter according to claim 2, characterized in that: the grid-connected reactor is connected to the U terminal of the three power units and the grid-connected switch, and the grid-connected reactor The reactor is a three-phase adjustable reactor, and the inductance value of the reactor is adjusted according to the current value of the power unit. 6. The high-voltage cascaded inverter power unit grid-connected feedback device according to claim 1 or 2, characterized in that: the control system is connected to the sampling part and the power unit, including sampling processing and grid-connected control unit, high-speed DSP calculation Unit, pulse control unit and man-machine interface, the sampling processing and grid-connected control unit filters and processes the sampling signal, and controls the grid-connected switch action at the same time; the high-speed DSP calculation unit uses the current control based on PI control in the synchronous rotating coordinate system Algorithm, calculate the output reference voltage signal, and output the calculation result to the pulse control unit for pulse management, communicate with the power unit through optical fiber, transmit control signals and receive operation information of the power unit.

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