A method applicable to four-quadrant control of electric forklifts

Abstract

The present invention discloses a method applicable to four-quadrant control of an electric forklift, comprising the following steps: Step 1: Calculate the busbar current idc; Step 2: Calculate the system power Pdc: According to the busbar current value idc and the busbar voltage Udc obtained in Step 1, calculate the system power; Step 3: Correct the speed given limit value according to the system power Pdc in Step 2. By calculating the busbar current, calculating the system power, and limiting the speed given value, the operation method of the present invention reduces the maximum speed given to the motor during slope charging, thereby effectively suppressing the risk brought by excessive braking power. Adopting single-integral regulation of the speed limit value can avoid a jump-like decrease in the speed given.

Description

Technical Field

[0001] The present invention relates to the technical field of electric forklift climbing and surging, and particularly relates to a method applicable to four-quadrant control of electric forklifts. Background Art

[0002] Electric forklifts adopt a speed control mode. During operation, they move forward and backward, and there are two working conditions of braking and traction in each movement direction. When the vehicle climbs a slope, different slopes result in different forward speeds. This is achieved by changing the output limit value of the speed loop. During traction, as the speed increases, the output torque passes through the torque limit and then gradually decreases. During surging, the torque is released to ensure that the vehicle can run stably downward at a fixed speed. In the existing technology, when the slope is large, the vehicle enters the surging state, and the braking torque required to maintain speed stability is relatively large; when the vehicle reaches a high speed, the braking power is too high. If the battery cannot recover energy in time, the capacitor voltage may be too high, leading to misjudgment of high voltage by the software, disconnection of the relay, and ultimately failure of the electronic control system. For example, Chinese Patent No. CN109910888 A discloses a vehicle downhill control method, device, and equipment. A vehicle downhill control method includes: obtaining the driving path information of the vehicle; monitoring whether there is a downhill slope in front of the current position of the vehicle based on the driving path information; if so, obtaining the slope length of the downhill slope in front of the current position of the vehicle; determining the target speed of the vehicle passing through the downhill slope based on the slope length; and when receiving a downhill control instruction, controlling the vehicle to pass through the downhill slope at the target speed. This patent application reduces the speed setting in advance by adding a device to predict the downhill in advance. Although this technology is feasible, the forklift industry is restricted by costs and does not increase the path detection cost casually.

[0003] Therefore, it has become a problem worthy of research to provide a method applicable to four-quadrant control of electric forklifts that can effectively suppress the risk brought by excessive braking power by reducing the maximum speed given to the motor during surging. Summary of the Invention

[0004] The object of the present invention is to provide a method applicable to four-quadrant control of electric forklifts that can effectively suppress the risk brought by excessive braking power by reducing the maximum speed given to the motor during surging.

[0005] The object of the present invention is achieved as follows:

[0006] A method applicable to four - quadrant control of an electric forklift, comprising the following steps: Step 1: Calculate the bus current \(i_{dc}\); Step 2: Calculate the system power \(P_{dc}\): According to the bus current value \(i_{dc}\) and the bus voltage \(U_{dc}\) obtained in Step 1, calculate the system power; Step 3: Correct the speed given limit value according to the system power \(P_{dc}\) in Step 2.

[0007] In the said Step 1, according to the instantaneous values of three - phase currents \(i\) U 、\(i\) V 、\(i\) W , and the working states of the three - phase bridge arms of the inverter \(S\) U 、\(S\) V 、\(S\) W calculate the current bus current value \(i_{dc}\), and the bus current calculation formula is as follows:

[0008] \(i\) dc = \(S\) U \(i\) U +\(S\) V \(i\) V +\(S\) W \(i\) W

[0009] Taking the direction of current flowing from the inverter into the motor as positive and the direction of current flowing from the motor to the inverter as negative;

[0010] Among them, the switch state \(S\) U ;

[0011] When the current is positive, the upper transistor is on, \(S\) U is 1, when the lower transistor is on it is 0, and when neither the upper nor the lower transistor is on it is 0;

[0012] When the current is negative, the upper transistor is on, \(S\) U is 1, when the lower transistor is on it is 0, and when neither the upper nor the lower transistor is on it is 0;

[0013] Similarly, deduce the switch states \(S\) V 、\(S\) W .

[0014] In the said Step 2, the calculation formula of the system power \(P_{dc}\) is as follows:

[0015] \(P\) dc = \(U\) dc *\(i\) dc

[0016] \(U_{dc}\) is the bus voltage, and the bus voltage \(U_{dc}\) is detected by a sensor, and \(i_{dc}\) is the bus current.

[0017] In step 3, the system power Pdc is used as a feedback link, and the preset system power threshold Pref is used as a given link. The single-integral regulation method is adopted, and the output limit value of the integral regulation is (0, -V). V represents the maximum correction value for correcting the given speed. The output speed given limit value of the integral regulation is corrected by gradually subtracting ΔV until the braking power is less than the preset value.

[0018] Positive and beneficial effects: By calculating the bus current, calculating the system power, and the operation method of limiting the speed given value, the maximum speed given by the motor during the slope rush is reduced, thereby effectively suppressing the risk brought by excessive braking power. The single-integral regulation speed limit value can avoid the jump-like decrease of the speed given. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a block diagram of the operation process of the present invention;

[0020] Figure 2 is a comparison block diagram of the operation process of the present invention and the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be further described below in conjunction with the drawings and embodiments.

[0022] Embodiment 1:

[0023] As Figure 1 and Figure 2 shown, a method applicable to the four-quadrant control of an electric forklift is characterized in that it includes the following steps: Step 1: Calculate the bus current idc; in step 1, according to the instantaneous values of the three-phase currents i U 、i V 、i W , and the working states S U 、S V 、S W of the three-phase bridge arm of the inverter, calculate the current value idc of the current bus, and the bus current calculation formula is as follows:

[0024] i dc =S U i U +S V i V +S W i W

[0025] Taking the direction of the current flowing from the inverter into the motor as positive and the direction of the current flowing from the motor to the inverter as negative;

[0026] where the switch state S U ;

[0027] When the current is positive, the upper tube conducts S UIt is 1 when the upper transistor is off, 0 when the lower transistor is on, and 0 when both the upper and lower transistors are off;

[0028] When the current is negative, the upper transistor conducts S U It is 1 when the upper transistor is off, 0 when the lower transistor is on, and 0 when both the upper and lower transistors are off;

[0029] Similarly, deduce the switch state S V 、S W 。

[0030] Step 2: Calculate the system power Pdc: According to the bus current value idc and the bus voltage Udc obtained in Step 1, calculate the system power; the calculation formula of the system power Pdc is as follows:

[0031] P dc =U dc *i dc

[0032] Udc is the bus voltage, which is detected by a sensor, and idc is the bus current.

[0033] Step 3: Correct the speed given limit value according to the system power Pdc in Step 2; in Step 3, the system power Pdc is used as a feedback link and the preset system power threshold Pref is used as a given link, and the method of single integral regulation is adopted. The integral regulation output limit value is (0, -V.). V represents the maximum correction value that can correct the given speed: the integral regulation output speed given limit value is corrected by gradually subtracting ΔV until the braking power is less than the preset value. The preset system power threshold is set in advance and should be less than the maximum braking power of the system, reducing the risk of excessive system braking power during the deceleration process.

[0034] When the system power is positive, it is a traction condition, the integral regulation output is 0, and the speed given value limit will not change. Different maximum torques corresponding to different speeds are used to make different slopes correspond to different climbing speeds; when the system power is negative, it is a braking condition. When the power reaches the preset value, the integral regulation takes effect and corrects the speed given limit value by gradually subtracting ΔV until the braking power is less than the preset value.

[0035] Embodiment 2

[0036] The difference between this embodiment and Embodiment 1 is only that: a bus current sensor is used to obtain the bus current, and the speed limit value is directly reduced by looking up a table according to the braking power.

[0037] The present invention reduces the maximum speed given by the motor during the slope rush through the operation methods of calculating the bus current, calculating the system power, and limiting the speed given value, thereby effectively suppressing the risk brought by excessive braking power. The single integral regulation of the speed limit value can avoid the jump-like decrease of the speed given.

Claims

1. A method applicable to four - quadrant control of an electric forklift, characterized in that: It includes the following steps: Step 1: Calculate the bus current \(i_{dc}\). According to the instantaneous values of the three-phase currents \(i_U\), \(i_V\), \(i_W\) and the operating states \(S_U\), \(S_V\), \(S_W\) of the three-phase bridge arms of the inverter, calculate the current value of the current bus \(i_{dc}\). The formula for calculating the bus current is as follows: \(i_{dc}=S_Ui_U + S_Vi_V + S_Wi_W\). The direction of the current flowing from the inverter into the motor is positive, and the direction of the current flowing from the motor to the inverter is negative; among them, the switching state \(S_U\); when the current is positive, the upper transistor is turned on and \(S_U = 1\), when the lower transistor is turned on, it is 0, and when neither the upper nor the lower transistor is turned on, it is 0; when the current is negative, the upper transistor is turned on and \(S_U = 1\), when the lower transistor is turned on, it is 0, and when neither the upper nor the lower transistor is turned on, it is 0; similarly, the switching states \(S_V\) and \(S_W\) are deduced; Step 2: Calculate the system power \(P_{dc}\): According to the bus current value \(i_{dc}\) and the bus voltage \(U_{dc}\) obtained in Step 1, calculate the system power. The formula for calculating the system power \(P_{dc}\) is as follows: \(P_{dc}=U_{dc}*i_{dc}\). \(U_{dc}\) is the bus voltage, which is detected by a sensor, and \(i_{dc}\) is the bus current; Step 3: Correct the speed given limit value according to the system power \(P_{dc}\) in Step 2. The system power \(P_{dc}\) is used as a feedback link, and the preset system power threshold \(P_{ref}\) is used as a given link. The single integral regulation method is adopted, and the integral regulation output limit value is \((0, -V)\): The integral regulation output speed given limit value is corrected by gradually subtracting \(\Delta V\) until the braking power is less than the preset value.

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