WO2010150236A2

WO2010150236A2 - Method for controlling the advancing speed in electrical propelled scooter

Info

Publication number: WO2010150236A2
Application number: PCT/IB2010/052923
Authority: WO
Inventors: Francesco Nepi
Original assignee: Oxygen S.P.A.
Priority date: 2009-06-26
Filing date: 2010-06-25
Publication date: 2010-12-29
Also published as: WO2010150236A3; ITRM20090334A1

Abstract

A method for controlling the advancing speed in electrical propelled scooter allows to control an electric scooter intuitively, practically and without creating any difficulty to the driver and comprises the steps of setting a target speed (v_t); detecting a real speed (v_r) of the electric motor (M) of the scooter; comparing the real speed (v_r) with the target speed (v_t); operating the electric motor (M) of the scooter so as to approach said target speed (v_t), by means of a PID controller (C_PID), the value of the proportional gain (K_p) thereof being variable according to a velocity error (ε_v) obtained by the step of comparing the real speed (v_r) and the target speed (v_t).

Description

"Method for controlling the advancing speed in electrical propelled scooter"

DESCRIPTION

The present invention refers to a method for controlling the advancing speed in electrical propelled scooter.

In view of an always higher attention to the environmental problems connected to the use vehicles equipped with fossil fuel motors and of the always increasing operation cost they require, the use of electrical propelled vehicles is becoming more and more diffused. A very interesting solution for the metropolitan areas is represented by electrical scooters, particularly suitable for transport services, e.g. postal ones, or home delivery.

Therefore, several managements began to substitute the internal combustion engine motorcycles with electrical propelled scooter, thus obtaining a undeniable advantage in terms of pollution and cost saving. Nevertheless, the features and the behaviours of these vehicles are for many aspects different from the traditional means of transport and, such differences can result in difficulties in driving the vehicle or, anyhow, be somehow troublesome. Furthermore, these difficulties can be dangerous and bothersome when the scooters are directed to transport services, in which high weights should be transported and the vehicle is subjected to continuous starts and stops. In fact, it can easily understood that as the two types of motor have remarkably different behaviours, they respond in a different way to the accelerator control offering very different sensations during driving. More precisely, a combustion motor offers a progressive behaviour, with a gradual increase of the torque, according to the characteristic curve of this kind of motors. Therefore, in order to obtain a soft start or a soft acceleration, in scooters equipped with internal combustion motors, it will be sufficient to gradually operate on the accelerator hand grip, directly adjusting the fuel supply to the motor.

Contrarily, in electrical scooters, in which a rotatable hand grip is still used for the accelerator control, the electric motor behaviour is defined according to the type of employed electronic control. I.e., upon rotating the hand grip, a control signal will be emitted which, by means of a suitable control design, will operate the electric motor.

According to the control method used, the motor behaviour will be different. A first possibility consist in implementing a torque control, conceptually in an analogous way as in combustion motor scooters. By operating on the accelerator the output torque to the motor will be varied and, consequently, also the vehicle speed.

Such control is subjected to the disadvantage that when the vehicle proceeds downhill, without operating on the accelerator, the motor will not produce any torque, while, on the contrary, it will required for the motor to automatically produce a breaking torque, so as to slow down the vehicle, analogously to the exhaust brake in internal combustion motors.

In order to avoid this drawback, it has been proposed to allow the accelerator to rotate according to two rotation senses, in a first case inducing positive torque, in the second case negative torque, thus operating the electric motor as a generator. Such solution is described in the International Patent Application n. WO 2003 078199. Nevertheless, also in this case, the use of the accelerator according to such method is little practical and, above all, hardly intuitive for a driver used to

^* drive traditional motorcycles. Moreover, such solution does not allow to best exploit the regenerative braking, i.e. the use of the motor as a generator for recharging the batteries with a consequent braking action, since the simple releasing of the accelerator only sets the torque to zero. On the contrary, it could be desirable to have a regenerative action even when the scooter is downhill or it is slowing down advancing on a plane road stretch, e.g. approaching a crossroad. In the system described in the above mentioned patent such action is assigned to the negative rotation of the accelerator, therefore to a little intuitive and spontaneous movement from the driver. Then, as an alternative it has been developed a velocity control system imposing the motor a determined velocity according to the rotation angle of the accelerator hand grip. Such solution solves the problems connected to the downhill advancing and to the little intuitiveness of the control, but it has the drawback to provide excessive rough accelerations, in particular on standing starts and at low speeds. In fact, such behaviour can be dangerous when the electric vehicle is used for transport and, consequently, heavy. Moreover, in general, it does not provide good sensations to the driver that substantially has the impression to have poor control of the vehicle.

. Hence, the technical problem underlying the present invention is to provide a method for controlling the advancing speed in electrical propelled scooters allowing to overcome the drawbacks mentioned above with reference to the known art. Such problem is solved by the method according to claim 1 and by the scooter according to claim 10.

The present invention provides several relevant advantages. The main advantage lies in that the method according to the present invention allows to s control an electric scooter intuitively, practically and without creating any difficulty to the driver. In addition, the method according to the present invention is particularly suitable to be integrated with a regenerative braking function, without the necessity of operating on specific commands.

Other advantages, features and the operation modes of the present invention io will be made apparent from the following detailed description of some embodiments thereof, given by way of a non-limiting example. Reference will be made to the figures of the encloses drawings, wherein: Figure 1 is a block diagram of the method for controlling the advancing speed in electrical propelled scooter according to the present invention; and i5 Figures 2A and 2B are two graphs showing examples of the function of the proportional gain and of the integral values variations of a PID controller, respectively, employed in the method according to the present invention.

Incidentally, the term scooter will mean that motorcycle category having the characteristic "step-through" shape, i.e. that can be crossed in the loweredo portion between the saddle and the front shield. Such vehicles are normally two-wheeled but, in some cases, three-wheeled and, the same inventive concepts that will be disclosed in the following could be applied also to this kind of vehicles.

With reference then to Figure 1, a block diagram summarizing the operation of5 the method for controlling the speed according to the present invention is shown.

In general, an electric scooter comprises an electric motor M, a control unit CU of the motor, in particular comprising the power stage and connected to the accelerator control A and, obviously, to the motor itself, and a battery pack BP for power supplying the scooter.

During scooter driving, the driver operates the accelerator control A so as to adjust the advancing speed of the vehicle, similarly to traditional motorcycles. In particular, for operating the accelerator A, the driver performs a rotation α of the hand grip thereof, such rotation having a determined amplitude relative to an initial resting position of the accelerator.

Then, according to modalities that will be described in deeper detail in the following, the amplitude of the rotation angle α will be transmitted to the control unit CU, which will associate such angle α to predetermined target speed v_t. In other words, the driver, by means of the rotation of the accelerator hand grip, selects a speed at which he wish to advance, denoted as target speed.

Such operation can be easily provided by using a potentiometer connected to the accelerator hand grip, so as to provide a signal variable according to the angle α. In the control unit CU the target speed v_t is compared with a real speed v_r corresponding to the real advancing speed of the scooter, which is e.g. detected by means of a speed sensor S_v, associated to the motor M. Such comparison operation allows to obtain a velocity error ε_v, obtained by the difference between target speed v_t and real speed v_r. As shown in figure 1, the control unit CU further comprises a PID controller Cpi_D of the velocity loop providing a control signal to the power stage and, consequently, performing the control of the motor.

As known, the PID controller performs a proportional, integral and derivative adjustment actions, adjusted according to the respective proportional gain K_p, integral gain K₁ and derivative gain K_d.

Therefore, the motor response is greatly affected by the values of such gains, in particular, a faster or slower response could be provided according to the regulation provided.

In the control method according to the present invention, the PID controller uses gains values, in particular K₁ and K_p ones, variable according to the velocity error ε_v.

In particular, the method according to the present invention provides that the gains K₁ and K_p values of the speed control loop vary so as to obtain a very fast response of the system when the velocity error ε_v is high, and instead it becomes gradually and automatically smoother upon the decrease of the error ε_v.

More precisely, faster responses and thus rougher behaviours corresponds to high Kp values and, for lower gain values, the system has a first order and slower dynamic response. Thus, for obtaining a smoother response it is preferable to diminish the proportional gain K₀ upon the decrease of the error ε_v.

Moreover, it has been experimentally seen that in order to obtain a more correct response, it is instead preferable to increase the integral value K₁ upon error ε_v decreasing. The control method of the advancing speed according to the present invention is accordingly based on a first step of setting the target speed v_t, operating on the accelerator control and, in particular, according to the angle α. At the same time, the real speed v_r of the scooter is detected by means of a suitable sensor S_v, the real speed v_r being compared with the target speed v_t. Then, the proportional gain K_p and integral gain K₁ values of the PID controller will be variable according to the velocity error ε_v, obtained by comparing the real speed v_r and the target speed v_t.

Then, the electric motor M of the scooter is operated, according to the proportional gain K_p and integral gain K₁ values, in a such way that the vehicle approaches the target speed v_t set by the driver.

By means of such control method, the scooter will decrease its acceleration when it is close to the target speed, thus providing a more intuitive and easier behaviour to be controlled by the driver. For example, in case that the scooter is steady and the driver desires to adjust the provided power in order to reach a determined velocity, he could notably accelerate in order to have a fast response. In fact, in this way the system will use high values of the proportional gain K_p since the error ε_v will be great. Instead, if the driver desires to obtain a smoother behaviour of the vehicle, he will gradually accelerate so as to set such lower K_p values and thus obtaining a smoother response.

With reference to the graphs of Figures 2A and 2B, showing a possible example of variation of the proportional gain K_p and of the integral gain K₁ values according to the velocity error ε, respectively, the variation method of the PID controller gains can be modified according to the determined velocity error. More precisely, as can be seen in the graphs, the trend of the proportional gain K_p and of the integral value K₁ are such that they remain constant for velocity errors lower than a minimum velocity error ε_vmιn and higher to a maximum velocity error ε_vmaχ, while they vary according to what has been previously described between such values. In this way, possible system instability are avoided, which can occur for excessively low or high gains K_p and K₁ values.

In addition, the variation method can be further modified for speed close to the maximum speed. In fact, in particular in this situation, the velocity error would become lower and lower upon approaching the maximum speed, thus providing slower and slower responses of the system. Therefore, in theory, the scooter will never reach the maximum speed. In order to overcome this drawback, it is possible to provide a different gains variation strategy, in particular at high speed. For example, it can be provided a function based on a multiplying coefficient of the real speed of the scooter or, in general, mathematical function can be used, diverting from the trend shown in figures 2A and 2B, taking into account of the problems connected to speeds close to the maximum one. Then, in other words, the proportional gain K_p and the integral value K, could vary according to the velocity error ε according to predetermined mathematical functions considering other parameters relative to the scooter motion.

Finally, it should be noted that the method according to the present invention provides the use of a torque controller transmitting a signal to the power stage according to a torque error analogously to what has been described for the speed loop. In this case, the target torque T_t will be set according to a signal provided by the PID controller, according to the velocity error and thus of the gains K_p, K₁, K_d thereof. By means of a suitable torque sensor S_τ a real torque T_r value of the scooter motor is detected, which is compared with the above mentioned target torque T_t, providing a torque error ε_τ.

Then, by means of the power stage the electric motor M of the scooter will be operated so as to provide the required target torque T_t. Therefore, it should be noted that, when the driver releases the accelerator, a zero target speed will be set, with a negative velocity error and the target torque to be set will be negative, thus correctly operating the motor as a brake. This aspect is then particularly advantageous when a regenerative braking system is employed, in which the batteries could be recharged when negative torque is required and the motor, in order to generate this breaking effect, operates as a generator.

The present invention has hereto been described with reference to preferred embodiments thereof. It is understood that there could be other embodiments referable to the same inventive kernel, all falling within the protective scope of the claims set forth hereinafter.

Claims

1. A method for controlling the advancing speed in electrical propelled scooter, comprising the steps of: a. setting a target speed (v_t); 5 b. detecting a real speed (v_r) of the scooter electric motor (M); c. comparing the real speed (v_r) with the target speed (v_t); d. operating the scooter electric motor (M) so that is approaches to said target speed (v_t), characterized in that said step of operating the electric motor takes io place by a PID controller (C_Pi_D), wherein the proportional gain (K_p) value of the PID controller (C_P]D) is variable according to a velocity error (ε_v) obtained by said step of comparing the real speed (v_r) and the target speed (v_t).

2. The method according to claim 1, wherein the proportional gain (K_p) i5 value is increased as said velocity error (ε_v) increases.

3. The method according to claim 1 or 2, wherein the value of the proportional gain (K_p) is such that:

• it is constant for velocity errors lower than a minimum velocity error (ε_vmιn) and higher than a maximum velocity error (ε_vmaχ);o • varies for velocity errors comprised between said minimum velocity error (ε_Vm_in) and said maximum velocity error (ε_vmax).

4. The method according to any of the preceding claims, wherein the integral gain (K₁) value of the PID controller (C_PID) is variable according to said velocity error (ε_v).

5 5. The method according to claim 4, wherein the integral gain (K₁) value is diminished as said velocity error (ε_v) increases.

6. The method according to claim 4 or 5, wherein the integral gain (K₁) value such that:

• it is constant for velocity errors lower than a minimum velocity error (ε_vmιn) and higher than a maximum velocity error (ε_vmaχ);

• varies for velocity errors comprised between said minimum velocity error (ε_vmι_n) and said maximum velocity error (ε_vmax)-

7. The method according to any of the preceding claims, wherein said step of setting a target speed (V_t) is achieved by operating the scooter accelerator (A).

8. The method according to claim 5, wherein said target speed (V_t) is associated to the rotation angle (α) amplitude of a an accelerator operating hand grip (A) of the scooter relative to an initial resting position.

9. The method according to any of the preceding claims, wherein said step of operating the electric motor (M) such that the vehicle approaches said target speed (v_t) comprises further steps of:

• setting a target torque (T_t);

• detecting a real torque (T_r) of the scooter electric motor (M); • comparing the real torque (T_r) with the target torque (T_t);

• operating the electric motor (M) so as to provide said target torque (T_t), said target torque (v_t) being determined according to a signal provided by said PID controller (C_Pi_D), according to the velocity error (ε_v) and to the consequently determined gains (K_p, K₁).

10.An electrical propelled scooter comprising an electric motor (M), a control unit (CU) of said motor (M), associated to an accelerator control (A) and to a battery pack (BP), said control unit comprising a PID controller (C_Pi_D) of the speed control loop, characterized in that the PID controller (C_P]D) gains (K_p, K₁) are adjusted by means of a method according to any of the preceding claims.