A hybrid energy control system and control method for electric forklift

Abstract

The present invention relates to a hybrid energy control system for an electric forklift, comprising a battery energy management unit, a lithium battery assembly, a motor controller, a relay and a motor; the battery energy management unit comprises a first controller, a first contactor and a super capacitor, and the lithium battery assembly comprises a second controller, a DC-DC low-voltage direct current power supply, a lithium battery module and a second contactor; the first controller communicates with the second controller and the motor controller respectively through a CAN bus. The present invention also discloses a control method for a hybrid energy control system for an electric forklift. The present invention solves the adverse effects of the peak power generated by the electric forklift at startup on the battery, and at the same time, the ability of the super capacitor to discharge rapidly can also make up for the insufficient power of the lithium battery; when the electric forklift brakes, the super capacitor can quickly recover the energy generated by braking due to its fast charging ability, thereby improving the energy recovery rate, and can also replenish the power of the lithium battery.

Description

Technical Field

[0001] The present invention relates to the technical field of electric forklifts, and in particular to a hybrid energy control system and a control method for an electric forklift. Background Art

[0002] Electric forklifts are slowly replacing internal combustion forklifts with their superior characteristics, but the development of electric forklifts is hampered by the short battery life and low battery energy utilization. Therefore, how to increase battery capacity and energy recovery rate is becoming increasingly important. At present, the energy recovery of electric forklifts mainly relies on the motor acting as a generator to convert mechanical energy into electrical energy to charge the battery when the forklift brakes, or the hydraulic drive generator converts gravitational potential energy into electrical energy when the gantry system descends. Since the working conditions of electric forklifts are more complicated and require frequent starting and braking, this is not conducive to the battery life and cell protection. Frequent starting and braking will cause over-power and over-current damage to the battery, which seriously affects the energy recovery and service life of the battery.

[0003] Supercapacitors are electrochemical components that store energy by polarizing electrolytes. They have a double-layer structure consisting of activated carbon porous electrodes and electrolytes, which allows them to have large energy storage space. The energy storage process does not chemically react and is reversible. They can be charged and discharged repeatedly for hundreds of thousands of times. They also have the characteristics of rapid charging and discharging with large currents. They have the characteristics of short current charging and discharging time, high specific power, high specific energy, long cycle life, and wide operating temperature. Therefore, they are suitable for the high current and large peak power characteristics of electric forklifts. Summary of the invention

[0004] The primary purpose of the present invention is to provide an electric forklift hybrid energy control system that solves the adverse effects of the peak power generated when the electric forklift is started on the battery, while compensating for the insufficient power of the lithium battery. When the electric forklift brakes, the energy generated by the brakes can be quickly recovered to improve the energy recovery rate and replenish the power of the lithium battery.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a hybrid energy control system for an electric forklift, comprising a battery energy management unit, a lithium battery assembly, a motor controller, a relay and a motor; the battery energy management unit comprises a first controller, a first contactor and a supercapacitor, the lithium battery assembly comprises a second controller, a DC-DC low-voltage DC power supply, a lithium battery module and a second contactor; the first controller communicates with the second controller and the motor controller respectively through a CAN bus.

[0006] The control end of the first controller is connected to the coil of the first contactor, the moving contact of the first contactor switch is respectively connected to the moving contact of the second contactor switch and the moving contact of the relay switch, the static contact of the first contactor switch is connected to the positive electrode of the supercapacitor, and the negative electrode of the supercapacitor is grounded with the negative electrode of the lithium battery module and the DC negative terminal of the motor controller; the control end of the second controller is connected to the coil of the second contactor, the static contact of the second contactor switch is connected to the positive electrode of the lithium battery module, the power supply end of the second controller is connected to the output end of the DC-DC low-voltage DC power supply, and the input end of the DC-DC low-voltage DC power supply is connected to both ends of the positive and negative electrodes of the lithium battery module.

[0007] The DC positive terminal of the motor controller is connected to the static contact of the relay switch, and the three-phase AC terminal of the motor controller is connected to the motor.

[0008] The first contactor and the second contactor are both DC contactors; and the motor is an AC motor.

[0009] Another object of the present invention is to provide a control method for a hybrid energy control system of an electric forklift, the method comprising controlling two processes of discharging and braking energy recovery of the electric forklift,

[0010] (1) Discharge process of electric forklift:

[0011] When the vehicle is started, the battery energy management unit obtains the SOC values ​​of the supercapacitor and the lithium battery module in real time. If the supercapacitor SOC value and the lithium battery module SOC value are both lower than 10%, the vehicle alarms that the battery power is too low and stops for charging.

[0012] If the SOC values ​​of the supercapacitor and the lithium battery module are both greater than 10%, the battery energy management unit communicates with the lithium battery assembly and the motor controller in real time via CAN. The control end of the first controller outputs a control current to power on the coil of the first contactor and close the switch of the first contactor. At the same time, the control end of the motor controller controls the relay switch to close, so that the discharge circuit is turned on, and the supercapacitor supplies power to the motor controller. The motor controller converts the DC power of the supercapacitor into three-phase AC power to drive the motor to operate. After waiting for the forklift to start, the first controller disconnects the switch of the first contactor, and at the same time, the control end of the second controller outputs a control current to power on the coil of the second contactor and close the switch of the second contactor. At this time, the lithium battery assembly supplies power to the motor controller.

[0013] If the SOC value of the supercapacitor is below 10% and the SOC value of the lithium battery module is higher than 10%, the first controller controls the switch of the first contactor to close, and the second controller controls the switch of the second contactor, so that the lithium battery module first supplies power to the supercapacitor and then to the drive motor;

[0014] If the SOC value of the supercapacitor is higher than 10% and the SOC value of the lithium battery module is lower than 10%, the first controller controls the switch of the first contactor to close, and the second controller controls the switch of the second contactor to close. At this time, the supercapacitor charges the lithium battery module, and then the two together provide power for the whole vehicle operation;

[0015] (2) Electric forklift braking energy recovery process:

[0016] When the vehicle brakes, the battery energy management unit obtains the SOC values ​​of the supercapacitor and lithium battery module in real time. If the detected SOC of the lithium battery module and supercapacitor are both lower than 10%, the vehicle will directly alarm that the battery power is too low and stop to charge.

[0017] If the SOC value of the lithium battery module is higher than 10% and the SOC value of the supercapacitor is lower than 10%, the first controller controls the switch of the first contactor to close, and the AC power generated by the drive motor is converted into DC power through the motor controller to charge the supercapacitor. At this time, if the power of the supercapacitor is still lower than 10%, the second controller controls the switch of the second contactor to close, and the lithium battery module continues to charge the supercapacitor until the power reaches the normal range;

[0018] If the SOC value of the lithium battery module is lower than 10% and the SOC value of the supercapacitor is higher than 10%, the second controller controls the switch of the second contactor to close. At this time, the electric energy generated by the drive motor is used to charge the lithium battery module first. If the SOC value of the lithium battery module is still lower than 10%, the first controller controls the switch of the first contactor to close, so that the supercapacitor charges the lithium battery module until it reaches the normal range.

[0019] If the SOC of the lithium battery module and the SOC of the supercapacitor are both greater than 10%, the battery energy management unit compares the SOC values ​​of the two and gives priority to charging the one with the lower SOC value until it is fully charged. If the lithium battery module is fully charged, the second controller controls the switch of the second contactor to disconnect; if the supercapacitor is fully charged, the first controller controls the switch of the first contactor to disconnect.

[0020] It can be seen from the above technical scheme that the beneficial effects of the present invention are as follows: First, under the working conditions of frequent starting and braking of electric forklifts, the present invention combines the advantages of supercapacitors with large current, large peak power, and fast charging and discharging, and the characteristics of lithium batteries with high energy density, and designs this system. On the one hand, it solves the adverse effects of the peak power generated by the electric forklift when starting on the battery. At the same time, the ability of the supercapacitor to discharge quickly can also make up for the insufficient power of the lithium battery. On the other hand, when the electric forklift brakes, the supercapacitor can quickly recover the energy generated by braking due to its fast charging ability, thereby improving the energy recovery rate and replenishing the power of the lithium battery; second, the present invention provides a control method using a supercapacitor as an auxiliary power source; third, the present invention combines the characteristics of supercapacitors and lithium batteries to invent an electrical principle of hybrid energy control to improve energy recovery efficiency; combined with supercapacitors and lithium batteries as power supply for the system, an energy control logic principle is invented. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the principle diagram of the control system of the present invention.

[0022] Figure 2 It is a flow chart of the control method of the present invention. DETAILED DESCRIPTION

[0023] like Figure 1 As shown, a hybrid energy control system for an electric forklift includes a battery energy management unit 1, a lithium battery assembly 2, a motor controller, a relay 6 and a motor; the battery energy management unit 1 includes a first controller, a first contactor 4 and a supercapacitor C1, and the lithium battery assembly 2 includes a second controller, a DC-DC low-voltage DC power supply, a lithium battery module B1 and a second contactor 5; the first controller communicates with the second controller and the motor controller respectively through a CAN bus 3.

[0024] The control end of the first controller is connected to the coil L1 of the first contactor 4, the moving contact of the switch K1 of the first contactor 4 is respectively connected to the moving contact of the switch K2 of the second contactor 5 and the moving contact of the switch K3 of the relay 6, the static contact of the switch K1 of the first contactor 4 is connected to the positive electrode of the supercapacitor C1, and the negative electrode of the supercapacitor C1 is grounded to the negative electrode of the lithium battery module B1 and the DC negative terminal of the motor controller; the control end of the second controller is connected to the coil L2 of the second contactor 5, the static contact of the switch K2 of the second contactor 5 is connected to the positive electrode of the lithium battery module B1, the power supply end of the second controller is connected to the output end of the DC-DC low-voltage DC power supply, and the input end of the DC-DC low-voltage DC power supply is connected to the positive and negative ends of the lithium battery module B1.

[0025] The DC positive terminal of the motor controller is connected to the static contact of the switch K3 of the relay 6, and the three-phase AC terminal of the motor controller is connected to the motor.

[0026] The first contactor 4 and the second contactor 5 are both DC contactors; the motor is an AC motor.

[0027] like Figure 2 As shown, the control method includes controlling the two processes of electric forklift discharge and braking energy recovery.

[0028] (1) Discharge process of electric forklift:

[0029] When the vehicle is started, the battery energy management unit 1 obtains the SOC values ​​of the supercapacitor C1 and the lithium battery module B1 in real time. If the SOC value of the supercapacitor C1 and the SOC value of the lithium battery module B1 are both lower than 10%, the vehicle alarms that the battery power is too low and stops for charging.

[0030] If the SOC values ​​of the supercapacitor C1 and the lithium battery module B1 are both greater than 10%, the battery energy management unit 1 communicates with the lithium battery assembly 2 and the motor controller in real time via CAN. The control end of the first controller outputs a control current to power on the coil L1 of the first contactor 4 and closes the switch K1 of the first contactor 4. At the same time, the control end of the motor controller controls the switch K3 of the relay 6 to close, so that the discharge circuit is turned on, and the supercapacitor C1 supplies power to the motor controller. The motor controller converts the DC power of the supercapacitor C1 into three-phase AC power to drive the motor to operate. After waiting for the forklift to start, the first controller disconnects the switch K1 of the first contactor 4, and at the same time, the control end of the second controller outputs a control current to power on the coil L2 of the second contactor 5 and closes the switch K2 of the second contactor 5. At this time, the lithium battery assembly 2 supplies power to the motor controller.

[0031] If the SOC value of the supercapacitor C1 is below 10% and the SOC value of the lithium battery module B1 is higher than 10%, the first controller controls the switch K1 of the first contactor 4 to close, and the second controller controls the switch K2 of the second contactor 5, so that the lithium battery module B1 first supplies power to the supercapacitor C1 and then to the drive motor;

[0032] If the SOC value of the supercapacitor C1 is higher than 10% and the SOC value of the lithium battery module B1 is lower than 10%, the first controller controls the switch K1 of the first contactor 4 to close, and the second controller controls the switch K2 of the second contactor 5 to close. At this time, the supercapacitor C1 charges the lithium battery module B1, and then the two together provide power for the whole vehicle operation;

[0033] (2) Electric forklift braking energy recovery process:

[0034] When the vehicle brakes, the battery energy management unit 1 obtains the SOC values ​​of the supercapacitor C1 and the lithium battery module B1 in real time. If the SOC values ​​of the lithium battery module B1 and the supercapacitor C1 are both lower than 10%, the vehicle will directly alarm that the battery power is too low and stop for charging.

[0035] If the SOC value of the lithium battery module B1 is higher than 10% and the SOC value of the supercapacitor C1 is lower than 10%, the first controller controls the switch K1 of the first contactor 4 to close, and the AC power generated by the drive motor is converted into DC power by the motor controller to charge the supercapacitor C1. At this time, if the power of the supercapacitor C1 is still lower than 10%, the second controller controls the switch K2 of the second contactor 5 to close, and the lithium battery module B1 continues to charge the supercapacitor C1 until the power reaches the normal range;

[0036] If the SOC value of the lithium battery module B1 is lower than 10% and the SOC value of the super capacitor C1 is higher than 10%, the second controller controls the switch K2 of the second contactor 5 to close. At this time, the electric energy generated by the driving motor is used to charge the lithium battery module B1 first. If the SOC value of the lithium battery module B1 is still lower than 10%, the first controller controls the switch K1 of the first contactor 4 to close, so that the super capacitor C1 charges the lithium battery module B1 until it reaches the normal range.

[0037] If the SOC of the lithium battery module B1 and the SOC of the supercapacitor C1 are both greater than 10%, the battery energy management unit 1 compares the SOC values ​​of the two and gives priority to charging the one with a lower SOC value until it is fully charged. If the lithium battery module B1 is fully charged, the second controller controls the switch K2 of the second contactor 5 to disconnect, so as to prevent the electricity generated by the motor from continuing to charge the lithium battery module B1 and causing overcharging of the lithium battery module B1; if the supercapacitor C1 is fully charged, the first controller controls the switch K1 of the first contactor 4 to disconnect, and energy recovery is prohibited at this time to prevent overcharging of the supercapacitor C1.

[0038] The following combination Figure 1 , 2 The present invention is further described.

[0039] The first controller communicates with the second controller and the motor controller in real time through the CAN bus 3 to obtain data from the lithium battery assembly 2 and the motor controller. At the same time, the first controller collects the power of the supercapacitor C1 in real time and controls the on and off of the switch K1 of the first contactor 4 to control the charging or discharging process of the supercapacitor C1. The first contactor 4 controls the on and off of the main circuit of the supercapacitor C1. The supercapacitor C1 is suitable for storing and releasing current, and can meet the charging and discharging requirements of instantaneous large currents. The lithium battery assembly 2 communicates with the battery energy management unit 1 and the motor controller through the CAN bus 3 to obtain the power data of the supercapacitor C1 in real time. The DC-DC low-voltage direct current power supply converts the high-voltage power supply of the lithium battery into a 12V or 24V low-voltage power supply to power the second controller. The lithium battery module B1 is a high-voltage, large-capacity battery module composed of multiple lithium battery cells in series and parallel, which can realize the charging and discharging process of long-term current. The second contactor 5 controls the on and off of the charging and discharging circuit of the lithium battery module B1 to realize the charging and discharging of the lithium battery module B1. The relay 6 is used to control the on / off of the discharge circuit of the motor controller. The motor controller converts the high-voltage direct current output by the super capacitor C1 and the lithium battery module B1 into three-phase alternating current to supply power to the motor.

[0040] When the motor starts, the system is in a discharge state. The first controller communicates with the second controller and the motor controller through the 6CAN bus 3. The motor controller sends the required current to the first controller and the second controller. At this time, the first controller first closes the switch K1 of the first contactor 4, and the motor controller controls the switch K3 of the relay 4 to close. At this time, the super capacitor C1 first outputs high voltage and high current to the motor controller to meet the high current demand when the motor starts. After starting, the first controller will disconnect the switch K1 of the first contactor 4, and the second controller will close the switch K2 of the second contactor 5. At this time, the lithium battery will continue to power the motor. At the same time, the second controller will communicate with the first controller through the CAN bus 3 in real time. When the power of the super capacitor C1 is too low, the lithium battery assembly 2 will replenish the power of the super capacitor C1.

[0041] When the vehicle brakes, the motor will act as a generator to generate AC power. At this time, the system is in a charging loop, and DC power will be formed after rectification by the motor controller. At this time, the first controller will close the switch K1 of the first contactor 4, and the second controller will open the switch K2 of the second contactor 5 to ensure that the supercapacitor C1 recovers the DC power. On the one hand, the charging efficiency of the supercapacitor C1 is higher than that of the lithium battery, which can improve the efficiency of electric energy recovery. On the other hand, the supercapacitor C1 has a higher charging capacity and can realize the recovery of electric energy in a short time. The power recovered by the supercapacitor C1 can be used as a preparation for the next discharge.

[0042] In summary, the present invention solves the adverse effect of the peak power generated when the electric forklift is started on the battery, and the ability of the supercapacitor to discharge quickly can also make up for the insufficient power of the lithium battery; when the electric forklift brakes, the supercapacitor can quickly recover the energy generated by braking due to its fast charging ability, thereby improving the energy recovery rate, and can also replenish the power of the lithium battery.

Claims

1. A control method for a hybrid energy control system of an electric forklift, characterized in that: The control system includes a battery energy management unit, a lithium battery assembly, a motor controller, a relay and a motor; the battery energy management unit includes a first controller, a first contactor and a super capacitor, and the lithium battery assembly includes a second controller, a DC-DC low-voltage direct current power supply, a lithium battery module and a second contactor; the first controller communicates with the second controller and the motor controller respectively through a CAN bus; The control end of the first controller is connected to the coil of the first contactor, the moving contact of the first contactor switch is respectively connected to the moving contact of the second contactor switch and the moving contact of the relay switch, the static contact of the first contactor switch is connected to the positive electrode of the super capacitor, and the negative electrode of the super capacitor is connected to the negative electrode of the lithium battery module and the DC negative terminal of the motor controller; the control end of the second controller is connected to the coil of the second contactor, the static contact of the second contactor switch is connected to the positive electrode of the lithium battery module, the power supply end of the second controller is connected to the output end of the DC-DC low-voltage DC power supply, and the input end of the DC-DC low-voltage DC power supply is connected to both ends of the positive and negative electrodes of the lithium battery module; The control method includes controlling the two processes of electric forklift discharge and braking energy recovery. (1) Discharge process of electric forklift: When the vehicle is started, the battery energy management unit obtains the SOC values ​​of the supercapacitor and the lithium battery module in real time. If the supercapacitor SOC value and the lithium battery module SOC value are both lower than 10%, the vehicle alarms that the battery power is too low and stops for charging. If the SOC values ​​of the supercapacitor and the lithium battery module are both greater than 10%, the battery energy management unit communicates with the lithium battery assembly and the motor controller in real time via CAN. The control end of the first controller outputs a control current to power on the coil of the first contactor and close the switch of the first contactor. At the same time, the control end of the motor controller controls the relay switch to close, so that the discharge circuit is turned on. The supercapacitor supplies power to the motor controller, and the motor controller converts the DC power of the supercapacitor into three-phase AC power to drive the motor to operate. After waiting for the forklift to start, the first controller disconnects the switch of the first contactor, and at the same time, the control end of the second controller outputs a control current to power on the coil of the second contactor and close the switch of the second contactor. At this time, the lithium battery assembly supplies power to the motor controller; If the SOC value of the supercapacitor is below 10% and the SOC value of the lithium battery module is higher than 10%, the first controller controls the switch of the first contactor to close, and the second controller controls the switch of the second contactor, so that the lithium battery module first supplies power to the supercapacitor and then to the drive motor; If the SOC value of the supercapacitor is higher than 10% and the SOC value of the lithium battery module is lower than 10%, the first controller controls the switch of the first contactor to close, and the second controller controls the switch of the second contactor to close. At this time, the supercapacitor charges the lithium battery module, and then the two together provide power for the whole vehicle operation; (2) Electric forklift braking energy recovery process: When the vehicle brakes, the battery energy management unit obtains the SOC values ​​of the supercapacitor and lithium battery module in real time. If the detected SOC of the lithium battery module and supercapacitor are both lower than 10%, the vehicle will directly alarm that the battery power is too low and stop to charge. If the SOC value of the lithium battery module is higher than 10% and the SOC value of the supercapacitor is lower than 10%, the first controller controls the switch of the first contactor to close, and the AC power generated by the drive motor is converted into DC power through the motor controller to charge the supercapacitor. At this time, if the power of the supercapacitor is still lower than 10%, the second controller controls the switch of the second contactor to close, and the lithium battery module continues to charge the supercapacitor until the power reaches the normal range; If the SOC value of the lithium battery module is lower than 10% and the SOC value of the supercapacitor is higher than 10%, the second controller controls the switch of the second contactor to close. At this time, the electric energy generated by the drive motor is used to charge the lithium battery module first. If the SOC value of the lithium battery module is still lower than 10%, the first controller controls the switch of the first contactor to close, so that the supercapacitor charges the lithium battery module until it reaches the normal range. If the SOC of the lithium battery module and the SOC of the supercapacitor are both greater than 10%, the battery energy management unit compares the SOC values ​​of the two and gives priority to charging the one with the lower SOC value until it is fully charged. If the lithium battery module is fully charged, the second controller controls the switch of the second contactor to disconnect; if the supercapacitor is fully charged, the first controller controls the switch of the first contactor to disconnect.

2. The control method of the hybrid energy control system for an electric forklift according to claim 1, characterized in that: The DC positive terminal of the motor controller is connected to the static contact of the relay switch, and the three-phase AC terminal of the motor controller is connected to the motor.

3. The control method of the hybrid energy control system for an electric forklift according to claim 1, characterized in that: The first contactor and the second contactor are both DC contactors; and the motor is an AC motor.

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