CN105227042A - The dead electricity of high-power high voltage frequency converter crosses over control method - Google Patents

Abstract

The invention relates to the technical field of electric energy conversion, in particular to a power-failure ride-through control method of a high-power high-voltage frequency converter. Whether the power grid is in the power-off state; if the power is off, the speed control loop of the vector control system is disengaged, and the torque current command value is set; the double closed-loop control mechanism of the DC voltage outer loop and the torque current inner loop is used to control the DC Voltage stable output; judge whether the power grid is restored, if restored, disengage the DC voltage control loop, and put into the speed control loop. This method does not need to change the existing main circuit topology and hardware parameters, and hardly increases the equipment cost; during the entire grid power failure period, the vector control algorithm is used to disengage the speed loop, and the torque current command value is directly set to zero ampere, avoiding The DC under-voltage fault is eliminated; the DC voltage control algorithm is used to stabilize the DC voltage by using the inertial energy of the motor shaft, avoiding under-voltage protection shutdown, and realizing power-off leapfrogging.

Description

Power failure ride-through control method for high-power high-voltage inverter

technical field

The invention relates to the technical field of electric energy conversion, in particular to a power-failure ride-through control method of a high-power high-voltage frequency converter.

Background technique

In recent years, the energy problem has attracted great attention from the state. Various electric motor loads are the largest consumers of electric energy and the users with the greatest potential for power saving. Key projects for energy saving and emission reduction. According to the national report "Study on Industrialization Approaches and Countermeasures of Motor Speed Regulation Technology", the total installed capacity of motors in my country has exceeded 580 million kilowatts, and 66% of the total power generation is consumed on motor loads. Since the design of the motor transmission system is to select the motor according to the maximum and the most severe working conditions, this unreasonable design requirement causes the actual operating load rate of the motor to be low. Since the flow is controlled by the baffle, the motor always outputs the rated power , resulting in a huge waste of electric energy. Therefore, it is very important to realize the overall goal of saving energy and reducing consumption by using high-voltage frequency converter to control the speed of the motor to adjust the flow.

In the practical application of the speed control system using high-voltage frequency converter, there are the following key problems: due to sudden load changes, various short-term symmetrical or asymmetrical short circuits, etc., the power grid will often have power failures of hundreds of milliseconds or even seconds. According to statistics, the probability of this kind of disturbance occurring in the power supply system is as high as 92% of all fault disturbances. This problem can lead to failure and downtime of the speed control system in normal operation, or cause equipment damage, which seriously affects the efficiency and quality of production.

Therefore, for high-quality high-voltage inverter products, if they have the spanning function during the short-term power failure of the power grid, and after the power grid is restored, they can quickly return to the working condition before the power loss of the power grid, which will have a wider range of applications. Application prospects, and this function is called "power failure spanning". To achieve this goal, the following two problems need to be solved:

It is necessary to carry out fast and accurate power failure detection.

Try to maintain the DC bus voltage so that it does not drop too much and cause undervoltage protection.

At present, due to different user requirements and load characteristics, there is no completely unified standard for power-off ride-through. There are mainly the following methods:

(1) By designing an internal model controller to control the output voltage and current of the speed-adjustable drive, experiments have shown that when the output of the controller can meet 2/3 of the load torque, the minimum allowable voltage drop value for the speed to recover is the original voltage 45%, the speed remains unchanged during the voltage drop, the minimum allowable voltage drop value is 20% of the original. However, this method is only suitable for the case where the voltage drop is relatively small and the drop time is not long, so it has certain limitations in application, and it is also highly dependent on the accuracy of the controller and circuit parameters.

(2) By changing the topology of the main circuit, for example, the front stage adopts full-controlled PWM rectification instead of uncontrolled rectification to maintain the DC bus voltage for a short time, and realizes the constant DC bus voltage by controlling the PWM rectifier. The maximum voltage drop that the circuit can withstand depends on the rectification The current rating of the bridge and the load of the system. However, the cost of this method is too high, the control is complicated, and the speed control system occupies a large space, which limits its practical application.

(3) Use energy storage technology to improve the ability of AC speed control system to withstand voltage drop, including: battery backup system, super capacitor system, motor-generator system, flywheel energy storage system, superconducting magnetic energy storage system, fuel cell. This method is the strongest energy storage method in terms of the ability to withstand voltage drops, but its cost is too high from an economic point of view, which is not conducive to general application.

Contents of the invention

In order to solve the above-mentioned technical problems, the present invention provides a power-failure ride-through control method for high-power high-voltage inverters based on the existing main circuit topology and hardware parameters, which can quickly and accurately judge power failure, and can avoid DC undervoltage faults.

The technical scheme of the present invention is, comprises the following steps:

Step 1): Determine whether the power grid is in a power-off state, and if so, perform step 2);

Step 2): disengage the speed control loop of the vector control system, and set the torque current command value;

Step 3): Adopting the double closed-loop control mechanism of DC voltage outer loop and torque current inner loop to control the stable output of DC voltage;

Step 4): Determine whether the power grid is restored, if not, return to step 3), and if so, perform step 5);

Step 5): Disengage the DC voltage control loop and put in the speed control loop.

Further, the method for judging the power-off state in the step 1) is as follows: compare the instantaneous value of the grid phase voltage sampled in this cycle with the sampled value of the previous sinusoidal cycle stored in the memory, and when the absolute value of the difference and If the total DC bus voltage reaches the power failure standard, it is considered that the power grid has lost power.

Further, the power loss standard is: the absolute value of the difference between the instantaneous value of the grid phase voltage sampled in this cycle and the sampled value of the previous sinusoidal cycle stored in the memory is greater than 5% of the rated value, and the total DC bus voltage is lower than 80% of rated value.

Further, the torque current command value in the step 2) is set to zero ampere.

Further, in the step 2), the stator flux linkage command value needs to be set to half of the rated command value.

Further, in the step 3), the specific way to control the stable output of the DC voltage by using the double closed-loop control mechanism of the DC voltage outer loop and the torque current inner loop is: set the DC voltage command of the power unit as a calibration value, according to the real-time The DC bus voltage value obtained by sampling is used to calculate the DC voltage deviation, and the torque current absorbed or emitted by the inverter is adjusted in real time through the PI control algorithm, so that the DC voltage is stably output at the calibrated value.

Further, in the step 3), the torque current command limit value of the double closed-loop control mechanism of the DC voltage outer loop and the torque current inner loop is [-1515].

Further, the grid recovery standard in step 4) is that the effective value of the phase voltage of the grid is greater than 90% of the rated value, and the total DC bus voltage is greater than 90% of the rated value.

Further, in the step 5), after disengaging the DC voltage control loop and putting in the speed control loop, set the motor speed command to be the speed value before the grid power failure, and restore the machine speed smoothly with a fixed acceleration.

Further, in the step 5), after the DC voltage control loop is disengaged, and the rotational speed control loop is switched on, the motor flux linkage command is set as a rated value, and the flux linkage is recovered smoothly at a constant acceleration.

Beneficial effects of the present invention: this method does not need to change the existing main circuit topology and hardware parameters, and hardly increases the equipment cost; the instantaneous value of the grid voltage combined with the DC voltage is used to detect the power failure of the grid, which is fast and accurate. Misoperation is avoided; during the entire grid power failure period, the vector control algorithm is used to disengage the speed loop, and the torque current command value is directly set to zero ampere, which avoids the DC undervoltage fault; the stator flux linkage command is set to the rated flux half of the chain value to avoid PWM over-modulation due to DC voltage drop; use the DC voltage control algorithm to use the inertial energy of the motor shaft to stabilize the DC voltage and avoid shutdown due to undervoltage protection; after the power grid is restored, only the motor speed and magnetic The chain can ensure that the speed control system returns to the stable operation of the working condition before the power failure, and realizes the power failure leap-forward.

Description of drawings

Fig. 1 is a control flowchart of the present invention;

Fig. 2 is a schematic block diagram of the high-voltage frequency conversion speed regulation system of the present invention;

Fig. 3 is a schematic block diagram of a speed sensorless vector control algorithm based on stator flux orientation;

Fig. 4 is a schematic block diagram of the DC voltage outer loop and torque current inner loop control strategy of the present invention;

Fig. 5 is a torque current waveform diagram;

Figure 6 is a waveform diagram of the DC voltage of the power unit;

Fig. 7 is a motor speed curve;

detailed description

In order to make the content of the present invention more clearly understood, the present invention will be further described in detail below according to the specific examples of the present invention and in conjunction with the accompanying drawings.

Taking the high-voltage frequency conversion speed regulation system in Fig. 2 as an example, the principle and practical implementation of the "power-off ride-through" control method proposed by the present invention will be described. As shown in Figure 1, the method shown in the present invention comprises the following steps:

Step 1): Determine whether the power grid is in a power-off state, and if so, perform step 2). In order to avoid starting the "power loss ride-through" control method in the shutdown or standby state, the premise of judging whether the power grid is in a power loss state is that the system is in normal operating conditions. To judge the power failure of the power grid, the traditional method uses grid voltage RMS detection or DC voltage detection, etc., but the detection and judgment time is often longer than 10mS, which may lead to DC undervoltage protection. The present invention detects the power failure of the power grid through the change of the instantaneous value of the grid voltage combined with the DC voltage value. The principle of the detection algorithm is: the instantaneous value of the phase voltage of the grid sampled in this cycle is compared with the sampled value of the previous sinusoidal cycle stored in the memory. , when the absolute value of the difference is greater than 5% of the rated value, and the total DC bus voltage is lower than 80% of the rated value, it is considered that the grid is out of power. Using the instantaneous value for judgment can ensure the rapidity of power loss detection, and the detection time of grid power loss is less than 1mS; at the same time, the criterion of DC voltage value is added to avoid misjudgment.

Step 2): Disengage the speed control loop of the vector control system, and set the torque current command value. Once the algorithm confirms that the power grid is out of power, it will immediately enter the "power loss leapfrogging" state machine. In this state machine, the control of Huocheng is mainly divided into "quick response", "power supply feedback and voltage stabilization control", and "grid incoming power speed recovery". three phases. Step 2) belongs to the "quick response" stage, which is carried out based on the sensorless vector control algorithm of the stator flux orientation. As shown in Figure 3, it is the principle block diagram of the speed sensorless vector control algorithm based on stator flux orientation. It can be seen from the figure that the process of this method is: the stator voltage obtained by AD sampling is carried out by Clark transformation and integral operation, and the stator flux linkage can be obtained. And the amplitude of the flux linkage; and then "digital phase-locking" the stator flux linkage to obtain the angular frequency ω _s of the stator flux and the sine value sinθ _s and cosine value cosθ _s of the rotation angle; the slip frequency ω _slip utilizes the torque The current and flux linkage are calculated, and then the motor speed ω _r can be estimated; the flux linkage amplitude, motor speed, and stator excitation current and torque current under the rotating coordinates are obtained, based on the flux linkage outer loop and the excitation current inner loop, The double closed-loop control algorithm of the speed outer loop and the torque current inner loop can realize the precise control of the motor speed. In the "quick response" stage, the following two operations need to be performed at the same time: a. Based on the vector control system in Figure 3, disengage the speed control loop and directly set the torque current command value to zero ampere, which can minimize the output of the inverter power to avoid DC undervoltage faults; b. Set the stator flux command to half of the rated flux value to avoid PWM over-modulation due to DC voltage drop. After the above two control objectives are achieved, due to the loss of the system, the DC voltage will still drop slowly, and then enter the stage of "voltage stabilization control for power generation and feedback".

Step 3): Using a double closed-loop control mechanism with a DC voltage outer loop and a torque current inner loop to control the stable output of the DC voltage. This step is the stage of "voltage stabilization control for power generation and feedback". Since the flux linkage is kept stable and the stator resistance loss is ignored during the grid power failure period, the relationship between the DC voltage and the stator current is:

$\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; Nu</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; C</span>}\frac{{\mathrm{<span\; class="notranslate">\; du</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; c</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; *</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;\&psi;i</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}$

Among them: N is the number of cascade units;

u _dc is DC voltage;

C is the support capacitance value;

R is the parallel resistance value of the DC bus;

Rs is the stator resistance value;

ω is the motor speed;

ψ is the amplitude of stator flux linkage;

i _q is the torque current value.

This formula shows that ωΨi _q is the released energy storage of the motor shaft. By controlling the magnitude of the torque current i _q (that is, indirectly controlling the amount of energy released by the motor shaft), various losses including DC resistance heating and stator resistance heating are compensated. After that, the DC voltage can be stabilized. Based on this conclusion, this program controls the motor to run in the state of power generation and energy feeding at this stage, and uses the inertial energy of the motor shaft to stabilize the DC voltage.

Fig. 4 is the principle block diagram of the DC voltage control strategy of the present invention. Fig. 4 adopts the double closed-loop control algorithm of the DC voltage outer loop and the torque current inner loop, and the PI output of the DC voltage outer loop is used as the instruction of the torque current inner loop. The power is relatively small. In this embodiment, the limit value of the torque current command is set to [-1515]. Set the DC voltage command of the power unit to 770V, the control system calculates the DC voltage deviation based on the DC bus voltage value obtained by real-time sampling, and then adjusts the torque current absorbed or sent by the inverter in real time through the PI control algorithm to achieve power Balance, and finally achieve the purpose of using the inertial energy on the motor shaft to ensure that the DC bus voltage of each power unit can be stabilized at around 770V during the power grid failure, and avoid undervoltage protection shutdown.

Step 4): Determine whether the power grid is restored, if not, return to step 3), if yes, execute step 5). The principle of detecting and judging whether the power grid is restored is: if the effective value of the phase voltage of the power grid is greater than 90% of the rated value, and the total DC bus voltage is greater than 90% of the rated value, the power grid is considered to be restored.

Step 5): Disengage the DC voltage control loop and put in the speed control loop. That is, the stage of "power grid incoming speed recovery", this stage is based on the vector control principle in Figure 3, and the following two operations are performed at the same time: a. Set the motor flux command as the rated value, and restore the flux at a speed of 10 Weber per second; b. Set the motor speed command as the speed value before the power grid failure, and restore the motor speed smoothly at a speed of 100r/min per second. When the motor speed error is less than 1r/min, the speed control system returns to the working condition before the power failure, and this "power failure spanning" is successfully completed.

The embodiment shown in Figure 4-6 is described with a 1MW high-voltage inverter, and the figure shows the torque current, power unit DC voltage, and motor speed variation curves during its operation. It can be seen from the figure that the power grid loses power at the 10th second, and the present invention quickly detects the power-off state through the instantaneous value of the grid voltage combined with the DC voltage value, and enters the power-off spanning working mode. First, the torque current is controlled to zero ampere through the torque current loop, and the flux linkage amplitude is controlled to 7.5 Weber through the flux linkage loop; after the control target is reached, the DC voltage loop is enabled and the DC voltage command value is set to 770V , use the energy of the motor shaft to offset the system loss, and ensure the stability of the DC voltage during the power grid failure. At the 15th second, the power grid is restored. In this embodiment, the initial value of the given speed is set to the current speed, and then the speed is gradually restored to the speed before the power failure at a rate of 100 r/min per second, and at the same time, it is rapidly increased at a rate of 10 Weber per second. Flux linkage to the rated value, it can be seen from the test results that the control method proposed by the present invention effectively overcomes the failure of the power grid, and the impact current is small.

The above is only a specific embodiment of the present invention. It should be pointed out that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention shall be covered by the protection scope of the present invention. within.

Claims (10)

1. the dead electricity of high-power high voltage frequency converter crosses over a control method, it is characterized in that, comprises the following steps:

Step 1): judge whether electrical network is in power failure state, if then perform step 2);

Step 2): the rotating speed control ring of throwing off vector control system, setting torque current command value;

Step 3): adopt direct voltage outer shroud, the double-closed-loop control mechanism of torque current inner ring, controls DC voltage stability and exports;

Step 4): judge whether electrical network recovers, and then returns step 3 if not), if then perform step 5);

Step 5): throw off DC voltage control ring, drop into rotating speed control ring.

2. the dead electricity of high-power high voltage frequency converter as claimed in claim 1 crosses over control method, it is characterized in that, described step 1) in power failure state determination methods as follows: the electrical network phase voltage instantaneous value of this periodic sampling and the sampled value of a upper sinusoidal cycles be stored in internal memory are made comparisons, when the absolute value of its difference and total DC bus-bar voltage all reach dead electricity standard, then think electrical breakdown.

3. the dead electricity of high-power high voltage frequency converter as claimed in claim 2 crosses over control method, it is characterized in that, described dead electricity standard is: the electrical network phase voltage instantaneous value of this periodic sampling is greater than 5% of rated value with the absolute difference of the sampled value being stored in the upper sinusoidal cycles in internal memory, and total DC bus-bar voltage is lower than 80% of rated value.

4. the dead electricity of high-power high voltage frequency converter as claimed in claim 1 crosses over control method, it is characterized in that: described step 2) in torque current instruction value be set as zero ampere.

5. the dead electricity of the high-power high voltage frequency converter as described in claim 1 or 4 crosses over control method, it is characterized in that: described step 2) in also need stator magnetic linkage command value to be set as the half of specified command value.

6. the dead electricity of high-power high voltage frequency converter as claimed in claim 1 crosses over control method, it is characterized in that, described step 3) in, adopt direct voltage outer shroud, the concrete mode that the double-closed-loop control mechanism control DC voltage stability of torque current inner ring exports is: the direct voltage instruction of setting power unit is calibration value, direct voltage deviation is calculated according to the d-c bus voltage value that real-time sampling obtains, adjust by PI control algolithm the size of torque current that frequency converter absorbs or send in real time, direct voltage is exported so that calibration value is stable.

7. the dead electricity of high-power high voltage frequency converter as claimed in claim 6 crosses over control method, it is characterized in that, described step 3) in, direct voltage outer shroud, the torque current instruction amplitude limit value of the double-closed-loop control mechanism of torque current inner ring is [-1515].

8. the dead electricity of high-power high voltage frequency converter as claimed in claim 1 crosses over control method, it is characterized in that, described step 4) in the standard of power system restoration be that the effective value of electrical network phase voltage is greater than 90% of rated value, and total DC bus-bar voltage is greater than 90% of rated value.

9. the dead electricity of high-power high voltage frequency converter as claimed in claim 1 crosses over control method, it is characterized in that: described step 5) in, throw off DC voltage control ring, after dropping into rotating speed control ring, the instruction of setting motor speed is the tachometer value before electrical breakdown, with fixing acceleration steadily extensive rotating speed of answering a pager's call.

10. the dead electricity of the high-power high voltage frequency converter as described in claim 1 or 9 crosses over control method, it is characterized in that: described step 5) in, throw off DC voltage control ring, after dropping into rotating speed control ring, the instruction of setting motor magnetic linkage is rated value, steadily recovers magnetic linkage with fixing acceleration.