CN110212543B - Power spring system considering non-critical load and control method thereof - Google Patents

Abstract

The invention discloses a power spring system giving consideration to non-critical loads and a control method thereof. The power spring system can detect the state of the non-critical load through the sensor so as to switch the working state of the power spring, and solves the problem that the power spring cannot run when the non-critical load is not connected or fails. Meanwhile, aiming at the problem that the voltage of a non-critical load in the power spring system possibly exceeds the limit operation range of the non-critical load, the invention provides a control method which can inhibit the voltage fluctuation of the critical load and can adjust the voltage of the non-critical load under the condition that the non-critical load exceeds the limit operation range, so that the non-critical load cannot be damaged or cannot normally work due to the fact that the non-critical load exceeds the limit operation range when the system works.

Description

An electric spring system and its control method taking into account non-critical loads

technical field

The invention relates to the field of application of power electronic devices in power systems, and relates to an electric spring system taking into account non-critical loads.

Background technique

With the continuous development of new energy power generation technology, the proportion of wind energy and other renewable energy connected to the grid is increasing year by year. Due to the inherent intermittency and uncertainty of renewable energy, it is difficult to predict the amount of electricity generated. The supply-demand relationship of the traditional power system may face power quality problems such as voltage fluctuations, flicker, and harmonic pollution in the face of high-permeability renewable energy access, jeopardizing the safe and stable operation of the power system. Especially for the microgrid, due to its limited adjustment ability, voltage fluctuations will have adverse effects on other electrical equipment. Especially for some precision equipment that has strict requirements on the input voltage range, such as vital sign detection equipment in hospitals, its unstable operation may cause huge loss of life and property. The proposal of the electric spring can effectively solve the above problems. According to the sensitivity of the load to voltage, the load can be divided into critical load and non-critical load. The voltage fluctuation on the critical load can be suppressed through reactive power compensation, and the fluctuation can be transferred to the non-critical load, thereby improving the power quality on the critical load.

The traditional power spring control can realize reactive power compensation by adjusting the output voltage of the power spring, stabilize the voltage on the critical load when the power supply voltage fluctuates, and at the same time transfer the voltage fluctuation to the non-critical load, so as to improve the power quality of the critical load the goal of.

Traditional solutions have not considered the failure or non-connection of non-critical loads, and the electric springs will not work properly at this time. At the same time, only the power quality on critical loads is considered and non-critical loads are ignored. Although non-critical loads allow a wide range of operating voltages, they cannot be sacrificed without limit, so regulation must be performed when non-critical loads exceed their voltage fluctuation range.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects of the prior art, and propose an electric spring system and its control method that take into account non-critical loads. On the one hand, the electric spring system and its control method considering non-critical loads proposed by the present invention can control the switch so that the electric springs can continue to work normally when the non-critical loads are not connected or fail. On the other hand, when the voltage on the critical load fluctuates, the electric spring can adjust the voltage through the method of reactive power compensation; at the same time, according to the maximum voltage fluctuation range that the non-critical load itself can accept, It is adjusted when the voltage is outside this range.

To achieve the above object, the technical scheme adopted in the present invention is as follows:

A power spring system that takes into account non-critical loads, including a switch drive circuit, a bidirectional DC power supply V _DC , a single-phase controlled voltage source inverter with two-level topology, and is used to filter out high-frequency components in the output voltage of the inverter The specific connection relationship of the system is as follows: the bidirectional DC power supply V _DC , the single-phase controlled voltage source inverter of the two-level topology and the LC low-pass filter together constitute the electric spring; the grid-side power supply V _G is connected to the common connection point PCC through the line impedance L ₀ and R ₀ , the electric spring is connected in series with the non-critical load Z _NCL through the filter capacitor C, and then connected in parallel with the key load Z _CL to the common connection point PCC; the switch S2 is connected in series with the filter capacitor C; As a bypass switch, S1 can switch the series part of switch S2 and filter capacitor C; switch S4 is connected in series with non-critical load Z _NCL ; switch S3 can switch the series part of switch S4 and non-critical load Z _NCL as a bypass switch switch; the controller in the inverter obtains the sensor signal to determine the working state, and drives the switch action through the drive circuit; when the switches S2 and S4 are closed and the switch S3 is open, the electric spring is switched by controlling the bypass switch S1; when When the non-critical load is not connected or the non-critical load fails, the switches S1, S2, and S4 are all disconnected, and the electric spring is directly connected in parallel with the key load to the common connection point PCC to ensure that the electric spring continues to work normally; when the electric spring part fails , the electric spring quits work, specifically when the non-critical load Z _NCL is connected and no fault occurs, the switches S1 and S4 are closed, and the switches S2 and S3 are opened, otherwise the switches S1, S2, S3, and S4 are all opened.

As a further improvement, the controller in the inverter detects the current flowing through the non-critical load Z _NCL through the current sensor to determine the access status of the non-critical load Z _NCL and whether a fault occurs.

A further improvement is to stabilize the voltage V _S across the critical load Z _CL by compensating reactive power; when it is detected that the voltage across the non-critical load Z _NCL exceeds its maximum fluctuation range, the non-critical load Z _NCL is limited by compensating active power The voltage across V _NCL fluctuates.

The above-mentioned control method of an electric spring system that takes into account non-critical loads includes the following parts:

(1) By collecting the current i ₂ flowing through the branch where the electric spring is located, a synchronous phase angle is generated through a phase-locked loop to provide a phase reference for the control circuit;

(2) The voltage sensor collects the voltage signal V _S of the common connection point, and the error signal e ₀ is obtained after making a difference between the reference signal V _{S_ref} and it, and the error signal e ₀ is transmitted to the proportional-integral PI controller and subjected to limiting processing to obtain the q-axis Voltage reference signal V _{ES_q} ;

(3) By detecting the voltage V _NCL on the non-critical load Z _NCL , judge whether the voltage V _NCL exceeds the maximum fluctuation range (V _lower , V _upper ) of the non-critical load itself; the voltage V _NCL on the non-critical load Z _NCL , The voltage upper limit V _upper and the voltage lower limit V _lower are sent to the comparator; when V ₀ is lower than the lower limit, V _lower and V _NCL make a difference to obtain an error signal e ₁ ; when V _NCL is higher than the upper limit, V _upper and V _NCL make a difference Get the error signal e ₁ ; if it does not exceed the maximum fluctuation range (V _lower , V _upper ), the comparator does not act, and the output error signal e ₁ is 0, that is, no adjustment is made; the error signal e ₁ is passed into the proportional integral PI control The reference signal V _{ES_d} of the d-axis voltage is obtained after the limiter is performed;

(4) After converting V _{ES_d} and V _{ES_q} and then performing limiting processing, the inverter output reference voltage V _{ES_ref} is obtained;

(5) Collect the voltage V _ES on the filter capacitor, make a difference between V _{ES_ref} and it to obtain an error signal and send it to the proportional resonant controller to obtain the inverter output reference voltage V _{ES_out} ;

(6) compare the reference voltage V _{ES_out} as the modulated wave of SPWM with the triangular carrier wave, and obtain the drive signal for controlling the on-off of the switching tube in the single-phase voltage source inverter at the point of intersection of the modulated wave and the carrier wave; When the non-critical load is connected and no fault occurs, the power P in the system satisfies the following formula:

P=P _NCL +P _CL (2)

Z _NCL is a non-critical load; Z _CL is a key load; V _S is the voltage of the common connection point PCC, which is also the voltage across the key load Z _CL ; V _ES is the output voltage of the electric spring, that is, the voltage on the filter capacitor; P _NCL is Active power consumed by non-critical loads; P _CL is active power consumed by critical loads.

As a further improvement, in the maximum fluctuation range (V _lower , V _upper ) of the non-critical load itself, the default upper limit is equal to 1.2 times the rated voltage, and the lower limit is equal to 0.8 times the rated voltage, which can be changed according to actual needs.

Compared with prior art, the beneficial effect that the present invention has is:

(1) Through the electric spring system and its control method that takes into account non-critical loads in the present invention, it can be realized that when non-critical loads are not connected or fail during operation, the electric springs still maintain normal operation and adjust critical loads to ensure that voltage fluctuations on critical loads are effectively suppressed.

(2) Through an electric spring system and its control method that takes into account non-critical loads in the present invention, it can be realized that when the voltage fluctuates, the voltage fluctuation on the critical load can be suppressed through reactive power compensation, and the fluctuation can be transmitted to non-critical loads. load. The control method proposed in the present invention considers that the voltage fluctuation on the non-critical load may exceed its maximum operating range, which may cause it to fail to work or be damaged, so an additional voltage loop is designed to adjust the voltage on the non-critical load. When the sensor detects that the voltage on the non-critical load exceeds the upper limit of its maximum operating range or is lower than the lower limit of the maximum operating range, it will limit its operating voltage within the maximum operating range by adjusting the active power. It can improve the voltage on the critical load while taking into account the voltage on the non-critical load to ensure the safe and stable operation of the system.

Description of drawings

Fig. 1 is a structural diagram of an electric spring system that takes into account non-critical loads in the present invention

Fig. 2 is a control block diagram of a control method of an electric spring system that takes into account non-critical loads in the present invention

Fig. 3 is an implementation flow chart of an electric spring system and its control method taking into account non-critical loads in the present invention

Fig. 4 is a phasor diagram of the parameters of each part of the circuit in the case of a resistive load after adopting a control method of an electric spring system that takes into account non-critical loads in the present invention.

detailed description

The electric spring system and its control method for non-critical loads according to the present invention will be further described in conjunction with the accompanying drawings.

The following is a best example of an electric spring system that takes into account non-critical loads according to the present invention, and does not limit the protection scope of the present invention.

Please refer to Figure 1, which shows an electric spring system that takes into account non-critical loads. An electric spring system that takes into account non-critical loads includes a switch drive circuit, a bidirectional DC power supply V _DC , and a single-phase receiver of a two-level topology. Controlled voltage source inverter, LC low-pass filter used to filter out the high-frequency components of the inverter output voltage; the specific connection relationship of the system is as follows: bidirectional DC power supply V _DC , single-phase controlled voltage of two-level topology The source inverter and the LC low-pass filter together constitute the electric spring; the grid-side power supply V _G is connected to the common connection point PCC through the line impedance L ₀ and R ₀ , and the electric spring is connected in series with the non-critical load Z _NCL through the filter capacitor C The key load Z _CL is connected in parallel to the common connection point PCC; the switch S2 is connected in series with the filter capacitor C; S1 is used as a bypass switch to switch the part connected in series between the switch S2 and the filter capacitor C; the switch S4 is connected in series with the non-critical load Z _NCL ; As a bypass switch, switch S3 can switch S4 and the non-critical load Z _NCL in series; the controller in the inverter obtains the sensor signal to determine the working state, and drives the switch action through the drive circuit.

Fig. 2 is a kind of control method of the electric spring system that takes into account non-critical loads in the present invention, and it mainly includes the following parts:

(1) By collecting the current i ₂ flowing through the branch where the electric spring is located, a synchronous phase angle is generated through a phase-locked loop to provide a phase reference for the control circuit;

(2) The voltage sensor collects the voltage signal V _S of the common connection point, and the error signal e ₀ is obtained after making a difference between the reference signal V _{S_ref} and it, and the error signal e ₀ is transmitted to the proportional-integral PI controller and subjected to limiting processing to obtain the q-axis Voltage reference signal V _{ES_q} ;

(3) By detecting the voltage V _NCL on the non-critical load Z _NCL , judge whether the voltage V _NCL exceeds the maximum fluctuation range (V _lower , V _upper ) of the non-critical load itself; the voltage V _NCL on the non-critical load Z _NCL , The voltage upper limit V _upper and the voltage lower limit V _lower are sent to the comparator; when V ₀ is lower than the lower limit, V _lower and V _NCL make a difference to obtain an error signal e ₁ ; when V _NCL is higher than the upper limit, V _upper and V _NCL make a difference Get the error signal e ₁ ; if it does not exceed the maximum fluctuation range (V _lower , V _upper ), the comparator does not act, and the output error signal e ₁ is 0, that is, no adjustment is made; the error signal e ₁ is passed into the proportional integral PI control The reference signal V _{ES_d} of the d-axis voltage is obtained after the limiter is performed;

(4) After converting V _{ES_d} and V _{ES_q} and then performing limiting processing, the inverter output reference voltage V _{ES_ref} is obtained;

(5) Collect the voltage V _ES on the filter capacitor, make a difference between V _{ES_ref} and it to obtain an error signal and send it to the proportional resonant controller to obtain the inverter output reference voltage V _{ES_out} ;

(6) compare the reference voltage V _{ES_out} as the modulated wave of SPWM with the triangular carrier wave, and obtain the drive signal for controlling the on-off of the switching tube in the single-phase voltage source inverter at the point of intersection of the modulated wave and the carrier wave;

As shown in FIG. 3 , it is a specific implementation of an electric spring system and its control method taking into account non-critical loads in the present invention. When the sensor detects that the voltage on the critical load fluctuates, the electric spring is activated to suppress the voltage fluctuation on the critical load Z _CL . When it is judged that the non-critical load Z _NCL is not connected or fails, the system operates in the non-critical load mode and only performs reactive power compensation. Otherwise, while compensating for reactive power, it is detected whether the voltage on the non-critical load Z _NCL exceeds its maximum fluctuation range (V _lower , V _upper ). If it exceeds the maximum fluctuation range, the electric spring will perform active power compensation. When the power spring part fails, the power spring quits working. Specifically, when the non-critical load Z _NCL is connected and no fault occurs, the switches S1 and S4 are closed, and the switches S2 and S3 are turned off; otherwise, the switches S1, S2, S3 and S4 are all turned off.

Fig. 4 is a phasor diagram of the parameters of each part of the circuit when the non-critical load is a resistive load in an electric spring system that takes into account non-critical loads in the present invention. It can be seen from the figure that while reactive power compensation is performed on the voltage on the critical load to stabilize the voltage on the critical load, the voltage on the non-critical load is adjusted to its operating range through active power compensation.

Claims (4)

1. A power spring system taking into account non-critical loads, characterized in that it comprises a bidirectional DC power supply V _DC and a single-phase controlled voltage source inverter of two-level topology, which is used to filter out the middle and high voltages of the inverter output voltage The LC low-pass filter of the frequency component, the power spring is connected in parallel with the key load Z _CL to the common connection point PCC through the filter capacitor C and the non-critical load Z _NCL ; the controller of the inverter in the power spring system passes the current sensor Detect the current flowing through the non-critical load Z _NCL to judge the access state of the non-critical load Z _NCL and whether a fault occurs, and control the switch to change the working state of the system according to the state of the non-critical load. 2. A kind of electric spring system taking into account non-critical loads as claimed in claim 1, characterized in that, the electric spring can be switched by controlling the bypass switch S1 when the switches S2 and S4 are closed and the switch S3 is open; When the non-critical load is not connected or the non-critical load fails, the switches S1, S2, and S4 are all disconnected, and the electric spring is directly connected to the common connection point PCC in parallel with the critical load; when the electric spring part fails, the electric spring quits work , which is specifically reflected in the fact that when the non-critical load Z _NCL is connected and no fault occurs, the switches S1 and S4 are closed, and the switches S2 and S3 are opened; otherwise, the switches S1, S2, S3, and S4 are all open. 3. A control method for an electric spring system that takes into account non-critical loads, characterized in that reactive power compensation is used to adjust the voltage on the critical loads to suppress voltage fluctuations on the critical loads, and when the voltage of the non-critical loads exceeds its maximum In the working range, the voltage on the non-critical load is adjusted by compensating the active power to ensure that the voltage is within the maximum working range; the control method mainly includes the following parts: (1) By collecting the current i ₂ flowing through the branch where the electric spring is located, a synchronous phase angle is generated through a phase-locked loop to provide a phase reference for the control circuit; (2) The voltage sensor collects the voltage signal V _S of the common connection point, and the error signal e ₀ is obtained after making a difference between the reference signal V _{S_ref} and it, and the error signal e ₀ is transmitted to the proportional-integral PI controller and subjected to limiting processing to obtain the q-axis Voltage reference signal V _{ES_q} ; (3) By detecting the voltage V _NCL on the non-critical load Z _NCL , judge whether the voltage V _NCL exceeds the maximum fluctuation range (V _lower , V _upper ) of the non-critical load itself; the voltage V _NCL on the non-critical load Z _NCL , The voltage upper limit V _upper and the voltage lower limit V _lower are sent to the comparator; when V ₀ is lower than the lower limit, V _lower and V _NCL make a difference to obtain an error signal e ₁ ; when V _NCL is higher than the upper limit, V _upper and V _NCL make a difference Get the error signal e ₁ ; if it does not exceed the maximum fluctuation range (V _lower , V _upper ), the comparator does not act, and the output error signal e ₁ is 0, that is, no correction is performed; the error signal e ₁ is passed into the proportional integral PI control The reference signal V _{ES_d} of the d-axis voltage is obtained after the limiter is performed; (4) After converting V _{ES_d} and V _{ES_q} and then performing limiting processing, the inverter output reference voltage V _{ES_ref} is obtained; (5) Collect the voltage V _ES on the filter capacitor, make a difference between V _{ES_ref} and it to obtain an error signal and send it to the proportional resonant controller to obtain the inverter output reference voltage V _{ES_out} ; (6) compare the reference voltage V _{ES_out} as the modulated wave of SPWM with the triangular carrier wave, and obtain the drive signal for controlling the on-off of the switching tube in the single-phase voltage source inverter at the point of intersection of the modulated wave and the carrier wave; When the non-critical load is connected and no fault occurs, the power P in the system satisfies the following formula:

P=P _NCL +P _CL (2) Among them, Z _NCL is a non-critical load; Z _CL is a critical load; V _S is the voltage of the common connection point PCC, which is also the voltage across the critical load Z _CL ; V _ES is the output voltage of the electric spring, that is, the voltage on the filter capacitor; P _NCL is the active power consumed by non-critical loads; P _CL is the active power consumed by critical loads. 4. A control method for an electric spring system that takes non-critical loads into consideration as claimed in claim 3, wherein the maximum fluctuation range (V _lower , V _upper ) of the non-critical load itself, the default upper limit is equal to the rated 1.2 times the voltage, the lower limit is equal to 0.8 times the rated voltage, which can be changed according to actual needs.

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