AU2021106929A4 - Novel Regenerative Braking for E-Rickshaw Application - Google Patents

Abstract

The present disclosure relates to a novel regenerative braking for E-Rickshaw application. A drive system has been developed which has capability to capture the kinetic energy of E Rickshaw using a novel logic technique. The novel logic is derived by using zero crossing of back EMF voltage of running vehicle. The peak EMF is detected and the semiconductor device of inverter lower leg is switched to achieve the boosting action to charge the battery during braking. The proposed novel technique results in less switching losses as only one device is switched for regenerative braking compared to conventional regenerative braking. 15 BATTERY BRAKE PADEL MO-TOR ELECTRONIC HYDRAULIC BRAKING SYSTEM Figure1I

Description

BATTERY BRAKE PADEL MO-TOR ELECTRONIC HYDRAULIC BRAKING SYSTEM

Figure1I

Novel Regenerative Braking for E-Rickshaw Application

Field of the Invention

The present divulgence relates to a Position Sensorless PMSM drive system for E Rickshaw application and a method of operation thereof. In particularly, this invention correlates to a novel regenerative braking for E-Rickshaw drive system.

BACKGROUND OF THE INVENTION

Electric vehicles are not new but being given focus nowadays due to very high pollution levels, zero emission policy, depleted fossil fuel and increasing running cost the gasoline driven vehicles. The concept of Electric vehicle was reported in the second quarter of 1 8th century. It is very difficult to pinpoint the development of first electric vehicle, however, in 1832-1838, an electric vehicle was reported in Hungry and at the same time, a crude electric Rickshaw was developed by British inverter Robert Anderson.

Thanks to William Morrison - US chemist who developed a six-passenger electric car capable to run around at its maximum speed of 22km/hours in 1890. It became very popular at that time in 1900 and around 30% vehicles in New York were electric vehicle at that time. The efficient Internal Combustion Engine introduced by Ford on 1908 has changed the mindset of people from electric vehicle to gasoline vehicle. The price of gasoline powered vehicle was one third of the price of electric vehicle, running cost gasoline vehicle was very low due to low price of fossil fuel and problems & limitations of EVs applied brake over electric vehicle and these vehicles disappeared after 1930.

Next 40-50 years, electric vehicle could not gain much popularity due to the problems associated with these vehicles like bulky battery with low energy density and no drive technology also low price of gasoline as well as availability of improved internal combustion engine at that time. Oil crises in around 1970, again given birth to the thought of electric vehicle. By the time, conventional gasoline vehicles continued to hitting the roads slowly. The increased quantity of these vehicle has given a jump in pollution level and it silently reached to alarming level in many metro cities.

The great attraction of researchers on electric vehicle was observed in 1990s when conventional gasoline vehicle targeted due to high pollution levels and the tremendous developments reported in the area of power electronics and digital controllers for electric vehicles for their retrieval. The major challenges faced by E-Rickshaw are summarised as:

• Higher cost of battery

• Limited battery life

• Longer charging time of battery

• Frequent charging requirement

• Unavailability of battery charging infrastructure

• Efficient Electric motor

• Advance Controllers

The most challenges are linked to the battery technology. It is expected that a small uplift in battery technology will certainly boost to the demand of electric vehicles. The batteries having good power density and low price, looks a very good candidate for EVs.

The basic characteristic requirement of an electric vehicle with respect to motor which is most critical item of an E-Vehicle are summarised as:

• High-power density & instant power

• Higher torque during starting & climbing at slow speeds

• Wider operating speed range with constant-torque and constant-power control modes

• Quick torque response

• Better efficiency over entire operating regions

• An efficient regenerative braking

• Good reliability and robustness

• Lower cost

The electric motors which are meeting these basic requirements are DC motor, Induction motor, PMBLDC motor, PM Synchronous Motor and S R Motor.

DC motors have ruled in the area of traction drive and still used in Electric Train of Indian Railways. The motor characteristic is ideally suited for an electric vehicle, but it has several drawbacks such poor efficiency, bulky size and frequency maintenance requirement due to commutator and brushes. DC motors are phased out from most application due to its associated problems.

With availability of vector control philosophy that converts characteristic of induction motor similar to DC motor, IMs have become a good choice for electric vehicle. The technology of these motors is matured and these are considered robust motors and being preferred widely for EVs and traction drives.

With advancement in Permanent Magnet (PM) technology, high efficiency PM machines have become reality. These motors are broadly classified into two main categories - PMBLDC

& PMSM. Both motors fulfil the basic requirement of EVs, therefore, being widely preferred most major EV manufacturer. These motors have highest power density, high toque density, maintenance free.

It is observed that Permanent Magnet Synchronous Motor (PMSM) is most efficient electric motor therefore it is selected for E-Rickshaw application in this disclosure. Table 1 present the comparison of Electric Motor for EV application.

Table 1 Comparison of Electric Motors for EV application

Feature Control Robustness Reliability Regenerative

Motor Capability

DC Easy Poor Poor Poor

IM Complex Very high Very high Good

PM Moderate Good High Best

SRM Complex Very high Very high Good

Synchronous Reluctance Motors also meet the basic requirement of EVs and these are also being used in EVs, but it has the problem of acoustic noise, therefore, less popular for EVs.

PMSM cannot be driven directly from an AC source like an Induction motor. It can be driven by an inverter. It also requires a position sensor to sense rotor position so-that stator phases can be excited to generate a driving torque at motor shaft. The position sensors are resolver or encoders. The rotor position is being sensed using these position sensors and inverter devices are gated accordingly. The position sensors are costly & bulky and radio interference issue; therefore, it forces restriction on PMSM to be used in compact electric vehicles as well as in hazardous areas. Use of position makes the drive system bulky, costly and less reliable. Therefore, a lot of work has been reported on position sensorless control of PMSM.

The sensorless control schemes are mainly divided into two major categories. One is adaptive and other one non-adaptive. The adaptive schemes are mainly consisting of sliding mode controllers and have the problems of chattering if no special technique is used to minimize the chattering. The back EMF based sensing requires less mathematical calculation and easy for implement and being used in electric vehicles

The E-Rickshaw being used in local transport are generally stop frequently due to heavy traffic in most metro cities as well as in other cities. E-Vehicles being used for public transport for short distance travel stops very frequency to pick-up and drop the passengers at their destination. Therefore, these vehicles are accelerated fast and stop very frequently and kinetic energy stored in running vehicle is wasted in braking if vehicle is not having energy recovery control in its drive system.

The regenerative braking is being utilised to recover the kinetic energy of vehicle to improve overall efficiency of drive system. The conventional braking topologies reported for PMSM drive system, uses two or more devices to conduct for braking implementation. The novel scheme uses only one device to conduct for implementation. Therefore, it reduces switching losses, hence, more efficient compared to conventional braking.

In general scenario all electric vehicle shall have regenerative braking to improve overall performance. The conventional existing braking needs improvement for making E-Rickshaw drive system more efficient.

In order to improve performance of regenerative braking in E-Rickshaw drive system a novel regenerative braking topology proposed.

Summary of the Invention

The present invention summary is easy to understand before the hardware and system enablement were illustrated in this present invention. There have been multiple possible embodiments that do not expressly point up in this method's present acknowledgment. Here, the conditions are used to explain the purpose of exacting versions or embodiments for understanding the present invention.

The present divulgence correlates to a position sensorless control of PMSM with novel regenerative braking for E-Rickshaw application. PMSM requires a position sensor for sensing the flux to enable the respective semiconductor devices of inverter to drive it. Inclusion of position sensor with PMSM increase the cost of motor, size of motor and reduces the reliability of drive system, therefore, the position sensorless control of PMSM is most essential for E Rickshaw application. The several position sensing topologies are reported but a perfect robust position sensing topology meeting electric vehicle drive system is still awaited. SOGI algorithm has been used in the PMSM drive system to estimate the rotor position.

The regenerative braking is common nowadays in most application as it improves overall efficiency of a drive system. The low-cost public transportation vehicle such as E-Rickshaw has built-in limited energy source and an efficient re-capturing of kinetic energy. The application of these vehicles involves frequent start & stop therefore an efficient implementation of regenerative braking in such vehicle becomes very-very vital. As every drop counts, similarly each efficiency regenerative braking boost the battery charge level cumulated over a period of 6-8 hours which is normal running of these vehicles per charging.

The propulsion drive motor is PMSM and it become Permanent Magnet Synchronous Generator (PMSG) while driven by the stored kinetic energy of vehicle. PMSM parameters are presented in Table-2. Due to permanent magnet excitation, three phase sinewave voltage is available which is proportional to the vehicle speed. For battery charging, the battery voltage must be less than peak of the terminal voltage. Therefore, for efficient recovery of vehicle kinetic energy an appropriate boosting mechanism is required.

Table 2 Parameters of PMSM

Parameter Name Value

Stator Resistance 0. 0166 Q

Stator Inductance 0. 223 mH

Voltage 30V

Rated Power 1000 W

Rated Speed 1200 RPM

Rated Current 38. 5 A

Rated Torque 8 N-m

Torque Constant 0. 141N-m/A

Back EMF Constant 13. 9 Vrms/K rpm

No of Poles 8

The present divulgence deals with novel regenerative braking topology for position sensorless PMSM drive system. In the disclosed topology, the inverter operation is disabled, on receipt of braking command. The zero crossings of terminal voltages are detected to enable the switching signal of inverter lower leg device having peak voltage. The release of switching signal, start boosting action and peak of the terminal voltage is made greater than battery voltage. The duty cycle of switching device is decided by the battery charging current, braking requirement and battery state-of-charge.

Brief Description of Drawings

These and other features, aspects, and advantages of the present divulgence will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure-1 illustrates the Overview of Disclosed E-Rickshaw Drive System.

Figure-2 illustrates the Block of Position Sensorless Control of PMSM Drive System - Driving

an E-Rickshaw.

Figure-3 illustrates the Block Diagram of Position Sensorless Control of PMSM Drive System

Regenerative Braking of an E-Rickshaw.

Figure-4 illustrates Block Diagram of Novel Regenerative Braking System.

Figure-5 illustrates a Control Logic Diagram of Novel Regenerative Braking for PMSM Drive

System.

DETAILED DESCRIPTION

This present invention is easy to understand with the reference of detailed figures and descriptions set forth herein. Here, various embodiments have been discussed regarding the architecture and flow chart. Some embodiments of this invention, illustrating its features, will now be discussed, and the disclosed embodiments merely exemplary of the invention that may embody in various forms.

Referring to Figure 1 illustrates the overview of E-Rickshaw drive system for which the invention in idented for. It presents the various components of drive system. The main electric components involve propulsion motor, inverter, battery and its controller. The three-phase inverter converts the battery voltage into three phase sine voltage to drive the motor. The controller is responsible for generating driving signal for inverter and boosting the terminal voltage for battery charging.

Referring to Figure 2 illustrates the schematic block diagram position sensorless control of PMSM for E-Rickshaw. It consists of Proportional-Integral (PI) speed regulator, PWM block responsible for firing pulse generation, current and voltage signals and its transformations. The switching pattern of each phase and DC link voltage are utilised for construction of the phase voltages. The position and speed of PMSM is being estimated using back EMF estimation algorithm. The E-Rickshaw drive system hardware consists of Insulated Bipolar Junction Transistor (IGBT) based three phase inverter, hall effect current sensors and PMSM coupled to drive E-Rickshaw. The speed reference command is given from pedal of vehicle in the form of voltage signal. It is connected to ADC channel of DSP controller and treated as speed reference after filtering and proper scaling. The estimated actual speed is fed to speed controller. Initial start is given by open loop ramp control algorithm and after attaining 30% of rated speed, drive system automatically switches to close loop control mode. The motor actual speed and reference speed signals are compared through a comparator. The speed error is fed to speed regulator which is responsible for reference torque generation. A limiter algorithm is utilised along with speed controller for safe operation of inverter switches. The torque reference command generated by speed controller is fed to toque controller. Hall effect sensors used for current sensing, produces voltage corresponding to running current. These signals are processed to alpha-beta stationary reference transformation and further converted to rotating d-q reference frame. The actual current & reference current are compared and current error is fed to PI torque controller. The direct axis current reference signal is kept zero below base speed. The outputs from flux & torque controllers are fed transformation algorithm for generation for reference vectors. The space vector modulation PWM algorithm accepts inputs from transformation blocks and switching pattern is being generated for power semiconductor devices with proper dead band. PMSM is being operated as generator in braking mode and kinetic energy is transferred to battery through boost control mode of drive system. The battery charging reference current is decided by user. The hall effect current sensor is used to sense battery current. PI controller decides the duty cycle of switching devices in boost control mode.

Referring to Figure 3 illustrates the drive system of E-Rickshaw includes a PMSM, an inverter, energy storage element and other associated control accessories. The three-phase inverter is controlled by DSP controller and three-phase AC voltages are being generated from battery voltage. The speed reference is decided by vehicle user. It is always started in open-loop and switch over to close loop speed control. The current flow path during motoring is shown in Figure 3. The direct axis current reference is kept zero to have maximum torque per ampere. The braking command is given by user as per requirement. The kinetic energy of vehicle is sent back to battery by regenerative braking. In regenerative braking mode, the inverter operates as boost chopper by firmware switching. The used specification of disclosed E-Rickshaw Drive System is given in Table 3.1.

Table 3.1 Specifications of Disclosed E-Rickshaw Drive System

CONTROLLER DETAILS

Clock Frequency 150MHz

PMW channels 16 Nos

Digital input 24Nos at 24V

INVERTER DETAILS Make of Device Infineon

Rated Voltage 1200V

Junction Temperature 150 0C

PMSM SPECIFICATION Rated Voltage 30V rms

Rated Power 1000kW

Rated Torque 8N-m

CURRENT SENSORS Make of sensor LEM, part no: CT50-T

Analog Output Voltage 5V

VOLTAGESENSOR Make of sensor LEM, part no: LV 100-100

Analog Output Voltage 100mA

Depending on speed reference, PI speed controller generates torque reference signal for current control loop. Starting position reference signal is generated through a ramp generator and after attaining speed greater than 20% rated speed, close loop speed control mode is enabled. Stator currents being sensed through hall current sensors are transformed into d-q rotating reference frame currents rotating with the rotor speed. Torque producing quadrature axis current reference is compared with measured rotor current and error is processed to PI current controller. Flux producing direct axis current reference is maintained zero. Reference to flux producing PI controller is always zero below base speed operation. The output of these quadrature & direct axis PI current controllers is voltage reference for to decide the switching of inverter. These quadrature & direct axis voltage reference signals are again transformed into three phase stator voltage reference frame signals and these references are processed to PWM generator. PWM unit generates gating signals for power semiconductor devices to drive the motor.

Referring to Figure 4 illustrates braking logic block diagram. The regenerative braking is very popular nowadays in battery powered electric vehicle. It plays very vital role in the E Rickshaw as it is public transport vehicle and has high starts & stop frequency. During the vehicle running, it stores the energy in proportion to mass and square of speed of vehicle. In case of conventional pedal / hydraulic braking, stored energy is wasted but in regenerative braking the stored kinetic energy is used for battery charging. It not only improves the overall efficiency of vehicle but also reduces the wear & tear of vehicle as negative torque is generative by motor to stop the vehicle.

The back EMF voltage waveforms are sinusoidal. In E-Rickshaw, propulsion motor is driven by battery. As a fundamental rule, battery voltage must be less than the back EMF voltage for charging of battery. Back EMF voltage induced in stator winding of PMSM is proportional to speed of motor. Back EMF voltage zero crossing is used for the preparation of regenerative braking logic. From the instant of application of brake, back EMF voltage starts decreasing, therefore, peak EMF detection becomes difficult in real-time. Innovative min-max logic is disclosed to detect peak EMF voltage for an efficient and effective regenerative braking mechanism.

In motoring mode, stator voltage generated by inverter leads motor back EMF voltage. Therefore, electric power is drawn from battery. When brake is applied, zero crossing of back EMF voltage is detected to initiate boosting mode and battery charges through diode in anti parallel to semiconductor devices. The negative electro-magnetic torque is produced at motor shaft at the instant of enabling of braking mode.

Referring to Figure 5 illustrates novel regenerative braking logic diagram. The voltage Vi & V2 which are positive peak and negative peak of back EMF voltage. The Vi & V2 are calculated as:

Vj= max Vy]* [VybI* [Vbl (1)

(Error! No m -[text of V2= min [VlY] *[Vybl *"[, specified style in document.)

The voltage V 3 & V 4 are intermediate voltages of regenerative braking logic and are calculated as:

V3= max[K] * [neg(V)] (3)

V4=mi [i]n * [neg(V)] (4)

The control logic signal VrVr, V-, Vy_, V., V_ are intermediate logic signals of regenerative braking logic and are calculated as:

Vr+= [ ] > 0.5* [ 3 1 (5)

Vy+= [yb > 0.5* [V31 (6)

Vb+= [b] > 0.5* [3] (7)

Vr-= [V] > 05 * [VY] (8)

vy_= [4] > 0.5 * [yb (9)

Vb= []> 0.5 * [Vbr] (10)

The switching signal for regenerative braking are derived in the form of Tr, Ty, T which are derived using below mathematical equations:

T = (Vr+)+(V y+*V)+(Vb+*V) (11)

Ty = (Vy+) +(Vb+*Vy-) +(Vr+*Vy-) (12)

Tb = (Vb+) +(Vr+*Vb-) +(Vy+*Vb-) (13)

EDITORIAL NOTE 2021106929

There is 1 page of claims only.

Claims (4)

WE CLAIM

1. A position sensorless control of PMSM with novel regenerative braking for E Rickshaw application, the system comprises of:

a controller module interconnected to the gate driver of inverter module, battery and PMSM through hall effect voltage & current sensors;

a back EMF based position estimator module for real-time position and speed estimation of PMSM; and

a novel regenerative braking module for efficient braking of PMSM.

2. The system as claimed in claim 1, wherein three phase inverter lower leg semiconductor device work as boost chopper for battery charging. The propulsion motor is Permanent Magnet Synchronous Motor for disclosed E-Rickshaw.

3. The system as claimed in claim 1, wherein the regenerative braking is derived from zero crossing of back EMF with the switching action of only one device which reduces the duty cycle of the switch i.e only 66% during braking.. Therefore a novel regenerative results in less switching losses with effective and efficient charging of battery during braking.

4. The system as claimed in claim 1, wherein the driving command converts battery voltage into variable frequency AC voltage and during braking, the back EMF is boosted utilised for battery charging. &

Figure 1

Figure 2

Figure 3

Figure 4

Vry V1 Vyb Max Vr- 2021106929

Vbr Tr

Vy- V2 V4 Ty Min K Min

K Vb- Tb

Vr+ V3 Max K K Vy+

Vb+

Figure 5